The Effects of Different Cooking Systems on Changes in the Bioactive Compounds, Polyphenol Profiles, Biogenic Elements, and Protein Contents of Cauliflower Florets

Abstract

In the current study, we examined the effects of boiling cauliflower in a pressure cooker, conventional boiling, conventional heating, and microwave heating on the chemical components, total phenol, flavonoids, antioxidant capacity (DPPH test), phenolic compounds, and mineral contents of cauliflower florets to reveal the differences between these cooking methods. Cauliflower is generally consumed either boiled or cooked in dry heat. In this study, different boiling and dry heat cooking methods were tried to reveal the changes in phytochemical composition and protein and mineral contents of cauliflower florets. Depending on the cooking methods of the cauliflower florets, the total phenolic and flavonoid contents of the cauliflower florets were determined to be between 273.72 (conventional heating) and 731.01 mg GAE/100 g (microwave heating) and 142.02 (conventional heating) and 797.10 mg/100 g (conventional boiling), respectively. The antioxidant capacity results of cauliflowers were found to be between 8.30 (conventional heating) and 33.69 mmol/kg (fresh). Statistically significant differences were detected in the moisture, total phenol, total flavonoid, and antioxidant activity values of cauliflower depending on the cooking techniques applied (p < 0.05). The gallic acid and 3,4-dihydroxybenzoic acid values of fresh and cooked cauliflowers were identified to be between 10.93 (microwave heating) and 194.79 mg/100 g (boiling in pressure cooker) and 17.58 (conventional heating) and 145.80 mg/100 g (boiling in pressure cooker), respectively. In general, the lowest amounts of phenolic compounds were defined in cauliflower samples boiled with a conventional heating system, followed by cauliflower samples cooked with the microwave heating method. Considering the component amounts as a result of cooking, the highest phenolic component amounts were specified in the cauliflower sample cooked by boiling in a pressure cooker. The protein quantities of fresh and cooked cauliflowers were determined to be between 16.11 (fresh) and 19.79% (microwave heating). The K and S contents of fresh cauliflowers and cauliflowers cooked with different blanching methods were specified to be between 19,647.62 (conventional boiling) and 35,130.01 mg/kg (conventional heating) and 3196.54 (boiling in pressure cooker) and 5105.65 mg/kg (microwave heating), respectively. The K, Mg, S, Fe, Cu, Mn, and Zn results of cauliflowers cooked in an oven and microwave were higher than those cooked using the control and boiling methods.

1. Introduction

Consumption of cauliflower, which belongs to the cruciferous family, is limited to florets. The parts of cauliflowers that are considered vegetables are given names such as the head, crown, flower, and inflorescence. Of these, the term crown is the most appropriate expression for cauliflower. Crown size in cauliflowers varies depending on sowing/planting time, planting density, and variety characteristics. Early or late planting and decreasing the distance between plants affect the crown size of cauliflowers [1]. Cauliflower covers an area of 8.88 million hectares in the world and has a production of 16.40 million tons [2,3]. Turkey ranks 7th among the cauliflower-growing countries. In the last five years, cauliflower production in Turkey increased by approximately 35,007 tons and 234,717 tons of cauliflower was produced in 2021 [4]. Due to mass and heat transfer during the thermal process, many chemical, biochemical, and physical changes occur after drying, which affect the quality characteristics of the products such as aroma, nutritional value, structure, and color [5]. A previous study determined the glucosinolate, polyphenol, and flavonoid contents and antioxidant activities of raw, steamed, and boiled cauliflower and detected glucoiberin, progoitrin, glucoraphanin, sinigrin, gluconapin, and eight glucosinolate peaks representing glucoiberverin, glucobrassicin, and gluconasturtin. Boiled cauliflower was reported to contain significantly lower glucosinolate, total polyphenols, and total flavonoids compared to raw or steamed cauliflower. These results suggest that the health-promoting compounds in cauliflower are significantly clearly shown to be affected [5]. These phenomena are mostly influenced by the duration and method of cooking, the type of vegetable matrix and the extent of cellular disruption, and the chemical structure of the glucosinolates [6]. Cauliflower is a widely consumed vegetable rich in glucosinolates, carotenoids, phenolic compounds, carbohydrates, proteins, and minerals such as copper, iron, selenium, calcium, manganese, and zinc. Cauliflower, which has a high nutritional value, contains an average of 0.418% P, 3.067% K, 0.247% Mg, 110.63 ppm Fe, 79.61 ppm Zn, and 68.43 ppm Mn [7,8,9]. In addition, by-products of cauliflower such as stems and leaves constitute an important source of bioactive compounds [8]. Fruits and vegetables constitute the main source of bioactive compounds [10]. Chain-breaking antioxidants are secondary metabolites that act as singlet oxygen deactivators, as well as free radicals responsible for initiating oxidation [11]. Cauliflower is used as the main ingredient in foods such as salads and soups. In addition, although fruits can be consumed raw, vegetables need to be cooked to enhance their flavor [12,13,14]. Brassica vegetables such as cauliflower and broccoli have been reported in many epidemiological studies to provide rich treatment, treatment of various types of cancer, and reduction of the risk of type 2 diabetes and disease [15,16] and are known to have strong antioxidant properties due to their polyphenol content [15,17,18,19,20]. Most vegetables belonging to the cruciferae family are considered to be good sources of natural antioxidants due to their high levels of phytochemicals [21]. Polyphenols are substances responsible for the coloring of plants. Polyphenol is seen in the branches, roots, seeds, and flowers of plants; in short, in all parts of plants. Phenolic compounds are secondary metabolites that are abundant in plants, and secondary metabolites are complex chemical components that have very important functions in plants [10,17,21]. Since cooking is a method of food preparation, if quality food is to be produced in every way, the chemical properties of nutrients and the principles applied in food preparation, cooking, and storage should be well known while cooking food, and care and attention should be paid in all applications. Incorrectly applied methods in preparation and cooking can cause vitamin losses, negative effects on the structure of proteins, and undesirable changes in the taste, color, and texture of the food [18]. Since cauliflower is generally consumed a lot in the winter season in Anatolia, this vegetable was preferred. As one can appreciate, the most common cooking methods for this vegetable are boiling and dry heat cooking in the oven. We tried to determine the changes in bioactive components, phenolics, antioxidant effects, and mineral contents of cauliflower florets by increasing the variety in these cooking methods. In this study, different boiling and dry heat cooking methods were tried to reveal the changes in phytochemical composition and protein and mineral contents of cauliflower florets. In Turkey, cauliflower is used boiled in the form of salads, fried, cooked in various ways, and pickled and frozen. Production and consumption of cauliflower is very common in developed countries. In recent years, the production and consumption of this vegetable has been increasing in Turkey. In recent years, there has been increasing interest in edible plants that are rich in secondary metabolites, often called phytochemicals, and in the antioxidant activity of such phytochemicals present in the diet. The aim of this study was to investigate the effects of boiling cauliflower in a pressure cooker, conventional boiling, conventional heating, and microwave heating on the chemical components, total phenol, flavonoids, antioxidant capacity (DPPH test), phenolic compounds, and mineral contents of cauliflower florets and to reveal the differences between these cooking methods.

2. Material and Methods

2.1. Material

Cauliflowers were sourced from a local greengrocer in Konya, Turkey in 2024. The cauliflowers transferred to the laboratory were washed. The florets were separated from the stem and leaf parts by hand and the florets were made ready for cooking. The chemicals used in this study were Methanol, Folin-Ciocalteu (Sigma), DPPH (Sigma), acetic acid (Merck, Germany), and acetonitrile.

2.2. Methods

2.2.1. Boiling and Heating Processes

During the boiling process in the pot, the cauliflower florets and water ratio was adjusted to 1:1; w/v and the cauliflowers were boiled in a pot at 100 °C for 13 min until they became tender. A total of 1 kg of cauliflower was put in a pressure cooker with 500 mL of water and the cauliflower florets were cooked at 120 °C for 6 min. The cauliflower florets (1 kg of florets) were placed in a Teflon tray in a row so that they did not touch each other and were cooked at 120 °C for 35 min. The florets were occasionally turned upside down during this cooking period. Similarly, the cauliflower florets (0.5 kg) were placed in a single row in a microwave tray and cooked in a microwave oven (Arçelik MD 595, TÜRKİYE) at 900 W for 12 min. During cooking, the microwave was turned off from time to time and the florets were quickly turned upside down at intervals so that they were cooked well.

2.2.2. Moisture Content

The moisture of cauliflower florets was established at 105 °C using an oven (Nüve FN055 Ankara, Türkiye) until they reached a constant weight [22].

2.2.3. Determination of Protein Contents of Cauliflower Samples

Protein amounts of the cauliflower florets were characterized according to AOAC [22] method.

2.2.4. Extraction Procedure

Extraction of cauliflowers was carried out according to Girgin and El [23]. After adding 20 mL of methanol/water (80:20, v/v) mixture onto 3 g of crushed cauliflower sample, the solution was stirred by a vortex (DZG SCIENCE MIX 2000 (TÜRKİYE) for 1 min and sonicated for 30 min. Then, it was centrifuged at 6000 rpm for 10 min. After repeating these steps twice, the extract was concentrated in an evaporator. The volume of the obtained extracts was made to be 10 mL via the addition of methanol (Merck). Then, it was filtered (0.45 µm).

2.2.5. Total Phenolic Content

The study of Yoo et al. [24] was taken into consideration in determining the total phenolic results of raw cauliflower florets and those cooked using various methods. Folin–Ciocalteu (1 mL) and Na₂CO₃ (10 mL) were added to extract and mixed with vortex. Deionized water was added until the final volume was 25 mL, and was kept in the dark for 1 h. Then, the absorbance was read at 750 nm. The results were recorded as mg gallic acid equivalent (GAE)/100 g (dw). The calibration graph equation and R² for total phenolic content are as follows: y = 0.0049x − 0.0002 R² = 0.9985.

2.2.6. Total Flavonoid Amount

Total flavonoid values of raw and cooked cauliflower florets were specified according to the method determined by Hogan et al. [25]. The cauliflower extract (1 mL) was mixed with 0.3 mL of NaNO₂, 0.3 mL of AlCl₃, and 2 mL of NaOH and kept in dark for 15 min. The absorbance was read at 510 nm. The findings were recorded as mg quercetin equivalent (QE)/100 g (dw). The calibration graph equation and R² for total flavonoid content are as follows: y = 0.0001x + 0.1577 R² = 0.9872.

2.2.7. Antioxidant Activity

The DPPH method used by Lee et al. [26] was used to establish the antioxidant activity of cauliflower extract. The extract was added to 2 mL of a methanolic solution of DPPH (1,1-diphenyl-2-picrylhydrazyl) and then vortexed and kept in dark for 30 min. After performing analytical procedures for antioxidant activity analysis, the absorbance was read at 517 nm. The results were recorded as mmol trolox (TE)/kg (dw). The calibration graph equation and R² for antioxidant activity are as follows: y = −0.7086x + 0.7229 R² = 0.9994.

2.2.8. Phenolic Compounds

HPLC (SCL-10 A VP-Shimadzu, Japan) instrument mounted with a PDA detector and an Inertsil ODS-3 (5 μm; 4.6 × 250 mm) column was used for the chromatographic separation of phenolic constituents in cauliflower extracts. A mixture of 0.05% acetic acid in water (A) and acetonitrile (B) were used as the mobile phase at a flow rate of 1 mL/min at 30 °C. The amount of sample injected into the device was 20 μL. Peaks from the extracts were captured at 280 °C using a PDA detector.

2.2.9. Determination of Minerals

After 0.2 g cauliflower parts were burned in a microwave device at 210 °C and 200 PSI pressure in 5 mL of concentrated HNO₃ and 2 mL of H₂O₂ (30% w/v), the volumes of the dissolved samples were made to be 20 mL via the addition of deionized water. Then, element concentrations in the cauliflower samples were analyzed with ICP-OES (Agient-5110, USA).

2.3. Statistical Analyses

The JMP statistical program was used for the statistical analysis of results. The variance analysis (ANOVA) was performed by averaging the triple analysis data of all transactions performed three times. The changes between the results of fresh and cooking methods were found to be significant and were determined by Duncan’s Multiple Range Test. The results were presented as the mean ± standard deviation of three independent experiments (n:3) (p < 0.05) [27].

3. Results and Discussion

3.1. The Moisture Contents and Bioactive Properties of Fresh and Cooked Cauliflower Florets

The moisture, bioactive compound, and antioxidant capacity values of fresh cauliflower florets and those cooked with different cooking methods (boiling in pressure cooker, conventional boiling, conventional heating, microwave heating) are offered in

Table 1. Bioactive properties of fresh and cooked cauliflower florets.

Cooking Method	Moisture Content (%)	Total Phenolic Content (mg GAE/100 g)	Total Flavonoid Content (mg/100 g)	Antioxidant Activity (mmol/kg)
Fresh	90.77 ± 0.54 * c	583.67 ± 17.25 b	357.01 ± 14.30 d	33.69 ± 0.62 a
Boiling in pressure cooker	94.18 ± 0.86 ab **	390.01 ± 11.89 c	409.10 ± 30.00 c	24.51 ± 0.41 c
Conventional boiling	94.48 ± 0.21 a	355.99 ± 12.06 de	797.10 ± 41.41 a	29.54 ± 0.47 b
Conventional heating	57.22 ± 0.11 d	273.72 ± 10.93	142.02 ± 11.54 e	8.30 ± 0.13 de
Microwave heating	36.54 ± 2.73 e	731.01 ± 13.02 a	452.35 ± 15.50 b	8.87 ± 0.02 d

* standard deviation; ** values within each column followed by different letters are significantly different at p < 0.05.

. Statistically significant changes were detected in the moisture, total phenol, flavonoid, and antioxidant activity results of the cauliflowers depending on the cooking techniques applied (p < 0.05). However, the moisture content of the cauliflowers was found to be similar in both the cauliflowers boiled in a pressure cooker and those cooked using conventional boiling. The moisture results of fresh and cooked cauliflowers were measured to be between 36.54% (microwave heating) and 94.48% (conventional boiling). Due to the phenolic compounds having contributed directly to the antioxidant action, it was necessary to investigate the total phenolic content. The initial level of total phenolic content in the fresh cauliflower was 583.67 mg GAE/100 g (on the basis of wet weight). The total phenolic and flavonoid values of cauliflowers cooked using different cooking methods were recorded to be between 273.72 (conventional heating) and 731.01 mg GAE/100 g (microwave heating) and 142.02 (conventional heating) and 797.10 mg/100 g (conventional boiling), respectively. The total flavonoids were significantly (p < 0.05) decreased by the conventional heating treatments compared to fresh cauliflowers and those cooked using other cooking methods. The highest value of total flavonoids was recorded for fresh cauliflower at 797.10 mg/100 g (dw). The amount of total flavonoids was significantly (<0.05) decreased by conventional heating treatments. The highest reduction was noted in cauliflowers cooked using conventional heating (about 60.22%). The methanolic extract of fresh cauliflower had significantly the highest DPPH radical-scavenging activity (33.69 mmol/kg), followed by the extracts cooked using conventional boiling (29.54 mmol/kg), boiling in a pressure cooker (24.51 mmol/kg), microwave heating (8.87 mmol/kg), and conventional heating (8.30 mmol/kg). Kenny and O’Beirne [28] indicated that the loss of antioxidant activity was relative to the contact area between vegetables and water as well as processing time. The antioxidant activities of raw and processed cauliflower, as determined by the DPPH radical scavenging method, are shown in Table 1. In the DPPH scavenging assay, the antioxidant activity was measured by the decrease in absorbance as the DPPH radical received an electron or hydrogen radical from an antioxidant compound to become a stable diamagnetic molecule [29]. In general, as a result of the applied cooking techniques, the moisture, total phenol content (except in the samples cooked using microwave heating), and antioxidant capacity values (except microwave heating) of cauliflower decreased significantly compared to those of fresh cauliflower.

An increase in the total phenolic result of microwaved cauliflower was observed compared to the fresh cauliflower sample. This increase may be due to the biochemical reactions occurring in cauliflower and the products formed as a result of the Maillard reaction, depending on the heat power and duration applied [28]. In other studies, since microwave heating preserves the active components in cooked tissue [30], the bioactive components of vegetables cooked in the microwave oven are generally higher than those of vegetables cooked in boiling water, which may be due to the fact that microwave cooking, grilling, and baking do not stimulate the release of ascorbic acid or other antioxidants from cooked tissue [31]. It is thought that the lower total phenolic content of the cauliflower sample in the conventional heating process compared to the microwave may be due to the slower moisture loss in the product during cooking compared to the microwave. Therefore, blanching processes (boiling in a pressure cooker and conventional boiling) can be considered preferred blanching methods, considering the bioactive components obtained in cauliflower and the analysis results. During cooking, some changes occur in the physical and chemical structures of vegetables. These phenomena are thought to be mostly affected by the cooking time and method, the type of vegetable, and the degree of cellular degradation and the chemical structure of the bioactive components. While the cooking process can destroy the phytochemicals of vegetables, it can also cause various effects such as their release and structural transformation. Some differences in the texture and nutritional properties of vegetables may result from the cooking processes. At the same time, cooking also causes losses in vitamins and antioxidant components and heat-sensitive compounds. The type of cooking process and the phytochemical composition of the cooked vegetable affect the extent of loss of phytochemicals in vegetables during cooking [12,13]. Cooking can affect not only the oxidation of phenolic compounds that show antioxidant activity in vegetables, but also the leaching of water-soluble compounds. Additionally, it has been reported that pro-oxidant enzymes are inactivated through heat treatment, which may therefore lead to increased antioxidant capacity [32]. Additionally, Maillard reactions occurring as a result of heat treatment can produce stronger antioxidant products [33]. Cauliflower contained 340.22 μg GAE/mg total phenol and 2.78 μg QE/mg total flavonoids [28]. The total phenolic and flavonoid results of cauliflower florets, respectively, were recorded as 2.76 and 0.29 mg RUT/g (dw) [34]. The antioxidant capacity and total phenolic results of raw, frozen, and heated cauliflowers were recorded to be between 3.73 (frozen) and 4.38% (raw) and 2.91 (heated) and 4.99 mg/dL (frozen), respectively [14]. The highest antioxidant capacity values of the methanolic extract of fresh, steam-blanched, steam-boiled, stir-fried, and microwaved cauliflower were 68.91%, 61.83%, 59.15%, 58.93%, and 58.24%, respectively [2]. Ahmed and Ali [2] determined the total phenolic initial amount of fresh cauliflower to be 782.43 mg/100 g (dw) and observed losses of total phenolic amounts after boiling and cooking the cauliflower (ranging from 15.6% to 51.9%, respectively). Ahmed and Ali [2] showed significant losses in the total flavonoid amount in cauliflower as a result of the cooking processes compared to the control (267.21 mg/100 g), and the highest loss was detected in cauliflowers boiled in water with 56.39%, followed by those boiled in water (43.42%) and pan fried, in decreasing order, followed by frying (30.23%). Since most bioactive compounds are easily soluble, they may be lost during cooking by passing into the cooking water [35]. The antioxidant activity (DPPH) values of raw and cooked cauliflower extracts varied between 35.13% and 68.91%, and the highest antioxidant capacity result was recorded in the methanolic extract of fresh cauliflower (68.91%), followed by 61.83%, 59.15%, 58.93%, and 58.24% in steam blanched, steam boiled, pan fried, and microwaved cauliflower extracts in decreasing order, respectively [2]. A previous study reported that the loss of antioxidant capacity in vegetables depends on the contact area between the vegetables and water and the processing time [36]. It has been reported that boiling, stewing, and steaming vegetables have detrimental effects on their total phenolic results and antioxidant activities [37]. In another study, while microwave cooking did not have any effect on the phenolic content of cauliflower, it was stated that it increased the antioxidant activity of cauliflower. In addition, boiling, steaming, and sous vide cooking reduced the amount of phenolic compounds [38]. Microwaving was better in terms of the retention of total phenolics than other cooking methods, while boiling significantly decreased the contents of total phenolics of vegetable products [39]. Also, steaming caused an increase in the total phenolic and antioxidant capacity values of vegetables, while boiling caused a decrease [23]. It is consistent with the literature data that generally applied heat treatment, especially boiling and boiling in water, causes losses in the bioactive components of cauliflower florets. However, although antioxidant activity values decrease with boiling and microwave heating, it has been reported in some studies that they increase due to the retention of antioxidant compounds in vegetables as a result of heat treatment [30]. Because microwave heating does not stimulate the release of ascorbic acid or other antioxidants from cooked vegetable tissue, the antioxidant activity of microwaved vegetables has generally been reported to be higher than that of those cooked in boiling water [31]. Generally, plant type, organ, developmental stage, drought stress, harvest time, other genotypic and phenotypic factors, and environmental factors can affect the phytochemicals and content profiles of plants [40,41].

3.2. The Phenolic Constituents of Fresh and Cooked Cauliflower Florets

The phenolic compositions of fresh cauliflower and cauliflower cooked using different cooking methods are offered in

Table 2. Phenolic compounds of the fresh and cooked cauliflower florets.

Phenolic Compounds (mg/100 g dw)	Fresh	Boiling in Pressure Cooker	Conventional Boiling	Conventional Heating	Microwave Heating
Gallic acid	146.18 ± 11.28 * c	194.79 ± 11.43 a	181.57 ± 11.35 b	24.17 ± 1.17 de	10.93 ± 0.98
3,4-Dihydroxybenzoic acid	103.43 ± 11.70 b **	145.80 ± 12.82 a	89.65 ± 8.69 c	17.58 ± 2.39 e	28.11 ± 1.81 d
Catechin	147.52 ± 15.02 c	482.03 ± 18.03 a	443.91 ± 17.43 b	79.75 ± 5.51 e	94.05 ± 7.57 d
Caffeic acid	46.87 ± 3.31 a	39.30 ± 0.79 b	36.84 ± 0.34 c	3.73 ± 0.36 e	15.05 ± 0.25 d
Syringic acid	66.84 ± 2.16 a	20.56 ± 0.35 c	20.32 ± 0.22 d	6.43 ± 0.94 e	20.75 ± 3.38 b
Rutin	148.72 ± 13.62 a	71.74 ± 2.83 b	40.86 ± 0.20 c	19.53 ± 1.05 e	31.73 ± 2.59 d
p-Coumaric acid	12.35 ± 0.25 a	4.78 ± 0.13 c	1.52 ± 0.02 e	2.20 ± 0.34 d	6.35 ± 0.68 b
Ferulic acid	19.85 ± 0.35 a	5.20 ± 0.07 c	3.84 ± 0.07 d	2.20 ± 0.11 e	7.34 ± 0.74 b
Resveratrol	1.27 ± 0.01 d	3.96 ± 0.05 a	2.99 ± 0.02 c	0.96 ± 0.06 e	3.09 ± 0.22 b
Quercetin	6.95 ± 0.17 a	2.91 ± 0.02 d	6.48 ± 0.04 b	0.63 ± 0.07 e	4.44 ± 0.47 c
Cinnamic acid	0.79 ± 0.02 b	1.73 ± 0.01 a	0.80 ± 0.01 b	0.39 ± 0.01 c	0.07 ± 0.01 d
Kaempferol	3.86 ± 0.05 c	5.04 ± 0.06 b	7.36 ± 0.15 a	0.53 ± 0.05 d	0.41 ± 0.07 e

* standard deviation; ** values within each row followed by different letters are significantly different at p < 0.05.

. Many polyphenolic constituents were specified in fresh, boiled, and oven- and microwave-cooked cauliflower florets. Several polyphenolic compounds were identified in cauliflower florets cooked by boiling, conventional and microwave heating, and boiling in a pressure cooker. These included gallic acid, 3,4-dihydroxybenzoic acid, catechin, caffeic, syringic, rutin, p-Coumaric acid, ferulic acid, resveratrol, quercetin, cinnamic acid, and kaempferol (Table 2). These compounds have been identified according to their retention time and the spectral characteristics of their peaks compared to those of standard compounds as well as by spiking the sample with standard compounds. The gallic acid and 3,4-dihydroxybenzoic acid values of fresh and cooked cauliflowers were characterized to be between 10.93 (in cauliflowers cooked via microwave heating) and 194.79 mg/100 g (in those boiled in a pressure cooker) and 17.58 (cooked via conventional heating) and 145.80 mg/100 g (cooked via boiling in a pressure cooker), respectively. While the catechin amounts of the cauliflower samples are recorded to be between 79.75 (conventional heating) and 482.03 mg/100 g (boiling in a pressure cooker), the caffeic acid amounts of fresh cauliflowers and those cooked using different cooking methods were defined to be between 3.73 (conventional heating) and 46.87 mg/100 g (fresh). Also, the amounts of syringic acid and rutin of the cauliflower samples were quantified to be between 6.43 (conventional heating) and 66.84 mg/100 g (fresh) and 19.53 (conventional heating) and 148.72 mg/100 g (fresh), respectively. The highest amounts of p-coumaric acid (12.35), ferulic acid (19.85), and quercetin (6.95 mg/100 g) were established in the fresh cauliflower sample. During cooking, the amounts of caffeic, syringic, p-coumaric, and ferulic acids and quercetin decreased compared to the fresh sample. Boiling in a pressure cooker and conventional boiling were better for the retention of phenolic compounds than other cooking methods, while conventional and microwave heating significantly decreased the contents of these compounds in broccoli and mushrooms. Phenolic compounds in vegetables are present in both soluble forms and combined with cell-wall complexes. Thus, an increased surface area of tissues in contact with cooking water and high cooking temperatures and lengthy cooking times are all likely to have caused disruption of the cell walls and the breakdown of phenolic compounds [42]. The highest loss was observed for cauliflowers cooked via conventional heating and microwave heating, averaging 76% and 66%, respectively. This could be due to the breakdown of phenolics or losses (leaching) during cooking, as most of the bioactive compounds are relatively unstable to heat and easily solubilized [20]. Considering the component amounts as a result of cooking, the highest phenolic component amounts were detected in the cauliflower sample cooked via boiling in a pressure cooker. However, there are some differences between the results of these two cooking methods. The reason why the phenolic compound amounts of cauliflower samples cooked with the conventional heating method are at the lowest levels may be due to the destruction of phenolic compounds due to the slow evaporation of the water content in the cauliflower during cooking. Since the time for this enzyme activity was a little shorter in the microwave heating process, the amounts of phenolic compounds were slightly higher compared to the conventional heating process. In the pressure cooker and conventional boiling systems, the structures of phenolic compounds were not destroyed much because the enzymes could not show much activity due to the short, low temperature period in the environment at the beginning of cooking. Considering that processing has a negative effect on phenolic contents, the highest losses were observed for boiling cauliflower. This could be due to the breakdown of phenolics, which are relatively unstable to heat and easily soluble, or losses (leaching) during cooking. Compared to the fresh cauliflower sample, the highest phenolic compound loss was detected in cauliflower samples cooked using the conventional and microwave heating methods. As with bioactive compounds, the highest amounts of phenolic constituents were determined in cauliflower samples cooked via boiling in a pressure cooker and conventional boiling systems. Statistical changes were monitored in the phenolic compound contents of cauliflowers depending on the cooking methods (p < 0.05). Raw cauliflower contained 86.4 alphacoumaric acid, 73.0 caffeine, 45.9 vanillic acid, 41.8 gallic acid, 36.60 catechol, 32.50 protocatechuic acid, 32.3 reversterol, 18.2 rutin, 16.6 quercetin, 15.3 naringinin, 14.60 apegenin, 13.9 kaempferol, and 13.8 mg/100 g hisperdin and 31.9 mg/100 g p-coumaric acid. The cinnamic acid values of boiled cauliflower and fresh cauliflower were not found to be statistically significant [43,44]. The protocatechuic acid, quercetin, pyrogallol, vanillic acid, coumaric acid, and kaempferol amounts of raw cauliflower analyzed by HPLC were 192.45, 202.4, 18.9, 11.90, 6.94, and 25.91 mg/100 g (dw), respectively [2]. The florets of raw and processed cauliflowers (mg/100 g (dw)) contained 0.66 (water boiling)-11.9 gallic acid (raw), 0.71 (steam boiling)-1.91 catechin (raw), 23.04 (water boiling)-192.4 protocatechuic acid (raw), 0.34 (water boiling)-4.90 catechol (raw), 8.14 (steam boiling)-25.83 chlorogenic acid (raw), 0.01 (water blanching) and (steam boiling)-2.57 rutin (raw), 0.21 8 water blanching)-1.64 caffeic acid (stir-frying), 22.35 (water boiling)-202.46 quercetin (raw), 1.54 (water boiling)-6.94 coumaric acid (raw), and 7.34 (water boiling)-25.91 kaempferol (raw) [2]. It has been reported that phenolic compounds remain in the edible portion of broccoli, possibly because steaming inactivates oxidative enzymes [43]. It has been reported that the retention of total phenolics during cooking of Boletus mushrooms in the microwave oven is better than that of other cooking methods, but boiling significantly reduces the total phenolic content of Boletus mushrooms [45]. Phenolic acids, which have the ability to dissolve in vacuoles and apoplasts [46], cause the release of these molecules into boiling water as a result of the softening and disintegration of cellular components during the cooking of vegetables [47]. While steaming and microwaving are better at retaining phenolic constituents than other cooking methods, a significant decrease in the content of these compounds in broccoli and mushrooms was observed with boiling [43,45]. Friedman [47] reported that this may be caused by polymerization resulting from the oxidation of polyphenols in vegetables during cooking, as well as covalent bonds between oxidized phenols and nitrogenous compounds such as proteins or amino acids. It has been stated that phenolic compounds, which are found in vegetables both in soluble form and combined with cell wall complexes, increase the surface area of their tissues with cooking water, and high cooking temperatures and long cooking times cause the cell walls to deteriorate and their structures to break down [48]. The most important factors affecting the amounts of phenolic compounds in Brassica vegetables include genotype, specific plant tissue, agronomic factors such as fertilization and irrigation, growing season, and some other environmental factors [49,50]. The results exhibited some differences based on cooking methods compared to the fresh cauliflower. The amounts of compounds other than the major phenolic compounds in cauliflower were found at very low levels (Table 2). In general, the lowest amounts of phenolic compounds were recorded in cauliflower samples boiled with the conventional heating system, followed by cauliflower samples cooked using the microwave heating method.

3.3. The Crude Protein and Biogenic Element Contents of Fresh and Cooked Cauliflower Florets

The crude protein and biogenic element contents of fresh and cooked cauliflower florets are illustrated in

Table 3. Macro and micro element mg (kg) and protein (%) contents of the fresh and cooked cauliflower florets.

Processes	P	K	Ca	Mg	S	Fe	Cu	Mn	Zn	B	Protein
Fresh	1961.87 ± 31.06 * e	30,296.99 ± 610.77 c	1664.52 ± 68.48 d	1018.60 ± 18.56 d	4081.68 ± 38.34 c	21.45 ± 0.19 e	2.40 ± 0.03 cd	7.58 ± 0.34 c	11.91 ± 0.10 c	1.69 ± 0.11 d	16.11 ± 0.43 e
Boiling in pressure cooker	2404.58 ± 90.75 a **	23,036.32 ± 1111.70 d	3000.35 ± 65.50 b	976.97 ± 25.82 e	3196.54 ± 141.11 e	31.15 ± 3.71 c	2.47 ± 0.50 c	6.75 ± 0.04 e	11.10 ± 0.42 e	2.90 ± 0.02 a	19.14 ± 0.71 c
Conventional boiling	2370.26 ± 103.31 d	35,130.01 ± 806.24 a	1603.91 ± 43.20 e	1181.37 ± 28.88 b	4603.52 ± 71.97 b	31.90 ± 0.51 b	2.68 ± 0.06 b	8.45 ± 0.35 b	14.21 ± 0.73 b	0.89 ± 0.01 e	18.03 ± 1.64 d
Conventional heating	2372.25 ± 87.76 c	34,131.42 ± 926.33 b	1746.22 ± 100.70 c	1223.30 ± 13.58 a	5105.65 ± 58.77 a	39.58 ± 1.30 a	3.17 ± 0.29 a	8.95 ± 0.37 a	15.96 ± 0.53 a	1.71 ± 0.01 c	19.79 ± 0.36 a
Microwave heating	2608.21 ± 99.66 b	19,647.42 ± 365.89 e	3380.59 ± 54.27 a	1054.98 ± 24.30 c	3299.24 ± 51.78 d	26.86 ± 0.47 d	2.68 ± 0.11 b	7.34 ± 7.34 d	11.89 ± 0.08 cd	1.91 ± 0.19 b	19.30 ± 0.08 b

* standard deviation; ** values within each column followed by different letters are significantly different at p < 0.05.

. The protein and element contents of fresh and cooked cauliflower samples showed some changes based on the cooking methods used. Boiling in a pressure cooker, conventional boiling, and microwaving significantly (p < 0.05) increased the protein contents of cauliflower florets. The highest (p < 0.05) increase in the protein content was observed for cauliflowers cooked via conventional heating. Statistical differences were observed in the mineral contents of the cauliflower depending on the cooking methods used (p < 0.05). No significant differences were found between the Cu contents of cauliflower cooked by conventional boiling and microwave heating. The element found in the highest amounts in cauliflower samples was K, followed by S, Ca, P, Mg, Fe, Zn, Mn, Cu, and B in decreasing order. The protein contents of fresh and cooked cauliflower florets were calculated to be between 16.11 (fresh) and 19.79% (microwave heating). The K and S amounts of fresh cauliflowers and those cooked using different blanching methods were found to be between 19,647.62 (conventional boiling) and 35,130.01 mg/kg (conventional heating) and 3196.54 (boiling in a pressure cooker) and 5105.65 mg/kg (microwave heating), respectively. Also, while the P amounts of the cauliflower florets are established to be between 1961.87 (fresh) and 2608.21 mg/kg (conventional boiling), the Ca amounts of fresh and cooked cauliflower samples were assessed to be between 1603.91 (conventional oven) and 3380.59 mg/kg (conventional boiling). The Mg amounts of the cauliflowers ranged between 976.97 (boiling in a pressure cooker) and 1223.30 mg/kg (microwave heating). The Fe and Zn values of fresh and cooked cauliflower samples were established to be between 21.45 (fresh) and 39.58 mg/kg (microwave heating) and 11.10 (boiling in a pressure cooker) and 15.96 mg/kg (microwave heating), respectively. The Mn amounts of the cauliflower samples ranged from 6.75 (boiling in a pressure cooker) to 8.95 mg/kg (microwave heating). During the boiling process, some of the minerals from the cauliflower florets were lost. However, conventional boiling processes provided the highest retention of the K mineral. In addition, it was observed that conventional heating provided more retention of the Mg, S, Fe, Cu, Mn, and Zn minerals compared to other cooking methods. Steam is generally expected to preserve more soluble nutrients than boiling. It is thought that mineral losses during cooking may be due to leaching into the cooking water, not destruction. The highest amount of B (2.90 mg/kg) was identified in the cauliflower sample cooked in a pressure cooker. The highest Mg, S, Fe, Cu, Mn, Zn, and protein contents were recorded in the cauliflower cooked in a microwave system. The amounts of P, Fe, Cu, and protein in cauliflower florets cooked with different cooking methods increased compared to the control. The K, Mg, S, Fe, Cu, Mn, and Zn contents of cauliflowers cooked with conventional and microwave methods were higher than those of the control and boiling methods. Since the behavior of minerals during blanching is related to their solubility, potassium, the most abundant mineral in vegetables, is extremely mobile and is easily lost by leaching during blanching because of its high solubility in water. Calcium and magnesium, which are usually bound to plant tissue, are not easily lost by leaching and can sometimes be taken up by vegetables during blanching from the processing water in areas with hard water [51]. It is thought that the element amounts in cauliflower samples blanched with both boiling methods are reduced because the elements pass into the boiling water during cooking. Mineral losses during the cooking of vegetables can occur not only by destruction but also by leaching into the cooking water [52]. The mineral increase in the cauliflower samples cooked by conventional and microwave methods may be due to the increase in element concentrations in the dry matter due to water loss in cauliflower during cooking. In a previous study, cauliflower, which has a high nutritional value, contains an average of 0.418% P, 3.067% K, 0.247% Mg, 110.63 ppm Fe, 79.61 ppm Zn, and 68.43 ppm Mn [6]. Raw cauliflower florets and those cooked via steam blanching, water blanching, steam boiling, water boiling, microwaving, and stir-frying contained 309 (Water boiling)-392 Na (raw), 2754 (water boiling)-3657 K (raw), 426 (water boiling)-480 Ca (raw), 405 (water boiling)-450 Mg (raw), 298 (water boiling)-329 P (raw), 706 (water boiling)-720 S (raw and microwave), 23.1 (water boiling)-25.3 Zn (raw), 1.87 (water boiling)-2.15 Mn (raw), and 20.1 (water boiling)-26.2 mg/100 g Fe (dw) (raw) [2]. While boiling resulted in high losses of bioactive compounds, phenolic compounds and mineral contents, stewing, steaming, microwaving, and even pressure steaming caused only minor losses [53], and mineral losses during cooking were mainly due to the penetration of minerals into the cooking water [54]. It has been reported that the potassium in vegetables is extremely mobile during boiling and is easily lost through leaching during boiling due to its high solubility in water. Statements in the previous study about losses in nutritional elements in vegetables during boiling and cooking confirm our results [2].

4. Principal Component Analysis

Principal component analysis (PCA) was carried out to reveal the effect of different heat treatments on the phenolic constituents, total phenolic content, total flavonoid content, and antioxidant capacity of cauliflower (Figure 1). PCA modeling exhibited about 50.278% of the explained variance for PC1 and 31.099% of the variance for PC2, which is given in

Table 4. PCA results in relation to bioactive properties of cauliflower.

	PC1	PC2
Eigenvalue	7.542	4.665
Variability (%)	50.278	31.099
Cumulative %	50.278	81.376
Correlation
Gallic	0.913	−0.375
Dihyd	0.902	−0.248
Catechin	0.648	−0.756
Caffeic	0.998	0.066
Syringic	0.669	0.738
Rutin	0.751	0.602
Coumaric	0.432	0.868
Ferulic	0.541	0.840
Resveratrol	0.323	−0.593
Quercetin	0.731	0.331
Cinnamic	0.683	−0.466
Kaempferol	0.825	−0.479
TPC	0.068	0.665
TFC	0.520	−0.412
AA	0.963	0.048

. All of the variables exhibited a positive correlation with PC1. Caffeic acid (0.998), antioxidant activity (0.963), gallic acid (0.913), and 3,4-dihydroxybenzoic acid (0.902) had a high positive correlation with PC1. PC2 was specified with coumaric acid (0.868) and ferulic acid (0.840). The highest gallic acid, 3,4-dihydroxybenzoic acid, and catechin values were observed in the sample cooked via BPC (boiling in a pressure cooker), followed by the sample cooked via CB (conventional boiling), which were located in both the positive area of PC1 and negative area of PC2. The fresh sample was located in the same area as syringic acid, rutin, quercetin, caffeic acid, coumaric acid, and ferulic acid, which were detected in highest level. Cauliflower florets cooked via MH (microwave heating) and CH (conventional heating) contained low amounts of phenolic compounds due to their location in different areas from these components. PCA results showed that the closest phenolic results to the fresh sample were obtained with the boiling process.

5. Conclusions

In this study, it was shown that boiling in a pressure cooker, conventional boiling, conventional heating, and microwave heating affect the composition, phytochemical contents, antioxidant activity, and phenolic profiles of white cauliflower florets. Conventional heating processes caused significant losses of total phenol, total flavonoid, and phenolic compounds as well as scavenging of the DPPH radical. In general, as a result of the applied cooking techniques, the moisture content, total phenol content (except in the samples cooked via microwave heating), and antioxidant capacity values (except in the samples cooked via microwave heating) of cauliflower decreased significantly compared to those of fresh cauliflower. Pressure cooking processes, boiling, and conventional cooking have caused significant losses. In general, the lowest amounts of phenolic constituents were detected in cauliflower samples boiled with a conventional heating system, followed by those cooked via the microwave heating method. Considering the component amounts as a result of cooking, the highest phenolic component amounts were detected in the cauliflower sample cooked via boiling in a pressure cooker. The highest Mg, S, Fe, Cu, Mn, Zn, and protein contents were recorded in the cauliflower cooked in a microwave system. The K, Mg, S, Fe, Cu, Mn, and Zn contents of cauliflowers cooked in an oven and via microwave were higher than those in the control group and those cooked via boiling.