Thermal Treatments Affect the Color, Water Activity, and Fatty Acid Profile of Cachichín Seed (Oecopetalum mexicanum) ^†

Abstract

Cachichín (Oecopetalum mexicanum) is a tree from Sierra de Misantla, Veracruz, Mexico, whose fruit produces a seed traditionally consumed raw, boiled, or toasted. This study evaluated the effects of three thermal treatments (boiling, commercial toasting, and controlled toasting) on the seed’s physicochemical properties, including color, water activity (αw), and fatty acid profile, using raw (unprocessed) seeds as a reference. Results showed that thermal treatments significantly altered αw, color, and lipid composition. Controlled toasting better preserved unsaturated fatty acids, while commercial toasting led to greater losses. These findings highlight the impact of processing methods on the seed’s nutritional quality and provide a basis for future research or applications.

1. Introduction

Mexico is considered a megadiverse country due to its richness in plant and animal species, hosting between 10% and 12% of world’s biodiversity. Surprisingly, around 7000 plant species have traditional uses [1]. Among these, more than 1500 are wild edible plants that can significantly contribute to the diet of rural families. However, many of these species remain underutilized due to a lack of awareness and information about their health benefits [2]. One such example is the seed of cachichín (Oecopetalum mexicanum Greenm. & C.H. Thomps.), which is produced in the Sierra de Misantla, Veracruz. This tree, belonging to the family Metteniusaceae, produces a green fruit that turns brown with a hard shell upon ripening. Inside this fruit is the seed, which is oval-shaped, with a thin, smooth-textured outer layer. Local producers value this seed and commercialize it, while residents of the region consume it raw, boiled, or toasted as a traditional and nutritious snack [3].

Thermal treatments (boiling, toasting, or frying) applied to seeds or grains tend to reduce enzymes such as lipases and lipoxygenases, thereby extending their shelf life [4]. However, thermal treatments have also been associated with protein degradation, changes in flavor and aroma, a reduction in microbial load, and even modifications to the structure of starch granules [5]. Changes in the structure of starch granules and the structural reorganization of proteins have been observed within the endosperm of cachichín seeds subjected to boiling and toasting treatments [6].

Water activity (αw) and color are important factors in the shelf life of food and consumer acceptance. These factors can be influenced by the thermal treatment applied before consumption, which tends to affect the texture, flavor, shelf life, and safety of food [7,8]. Additionally, identifying and quantifying lipids, specifically fatty acids in cachichín seeds, is crucial because these compounds play a fundamental role in their nutritional and functional value [3]. Unsaturated fatty acids, such as oleic (ω-9), linoleic (ω-6), and linolenic (ω-3) acids, are of particular interest due to their health benefits [9]. However, these fatty acids can undergo degradation or modification during the application of thermal treatments, which may affect both the nutritional quality and the physical properties of the final product [10]. Therefore, this study aimed to evaluate how different thermal treatments applied during the processing of cachichín seeds for consumption impact their physicochemical properties, the quality of the final product, and their potential application in the food industry.

2. Methods

2.1. Raw Material Procurement

The cachichín seeds (Oecopetalum mexicanum) were obtained from a collective of producers and local vendors in Misantla, Veracruz. The study evaluated raw seeds (T1), boiled seeds (T2), seeds subjected to commercial toasting (T3), and seeds subjected to controlled toasting (T4), as shown in Figure 1. Treatments T2 and T3 were carried out using traditional and empirical thermal processes by producers from the study region. T2 was obtained by boiling the seeds in a stainless-steel container over direct heat until reaching boiling point for at least one hour. For T3, the seeds were toasted on a clay or red earthenware griddle from the Sierra de Misantla at temperatures ranging from 250 to 350 °C for 60 to 90 min over low heat. The completion of the toasting process was determined based on visual and sensory indicators traditionally used by local producers, such as the development of a uniform golden-brown color and a characteristic toasted aroma. These indicators ensured consistency and alignment with traditional practices. It is important to note that both treatments, T2 and T3, used firewood from local trees as the primary heat source.

Controlled toasting (T4) was performed using an aluminum pan equipped with a modified lid connected to a crank-operated propeller that maintained constant rotational movements to replicate traditional toasting. Heat was supplied using a heating plate (Thermo-Scientific SP131015Q, Waltham, MA, USA) at a temperature of 134 °C for 25 min following a method described elsewhere [6]. Finally, after the boiling and toasting processes, all treatments underwent dehulling, and the seeds were stored at room temperature (approximately 13–14 °C, according to the average climate of Montecillos, Texcoco, State of Mexico, Mexico) for a variable period of 7 to 10 days before analysis.

2.2. Determination of Water Activity and Color

Water activity (αw) was measured based on the methodology described by the AOAC [11] using an Aqualab Series 3TE device (USA). Color determination was performed with a Hunter-Lab colorimeter (Hunter Lab, Reston, VA, USA), obtaining lightness (L*) and the chromatic coordinates a* (red/green) and b* (yellow/blue). Additionally, the total color change (∆E) was quantified using Formula (1), where a value close to 0 indicates better color retention. The intensity or saturation of color, expressed as chroma (C*), was calculated using Formula (2). The Hue angle (H°) was calculated using Formula (3); which describes the perception of color. Hue angle values of 0°, 90°, 180°, and 270° correspond to pure red, yellow, green, and blue, respectively.

∆E = √((L* − L₀)² + (a − a₀)² + (b − b*₀)²)

(1)

C* = √(a² + b²)

(2)

H° = tan⁻¹(b*/a*)

(3)

2.3. Fatty Acid Profile

Prior to the analysis, oil extraction was performed following the methodology established by Hernández-Mora et al. [12]. An automatic extrusion extraction device (3–5 kg, Preenex, Shanghai, China) preheated to 250 °C was used. The obtained oil samples were placed in hermetically sealed tubes, wrapped in aluminum foil, and stored in a refrigerator (LG GR-389SQF, Monterrey, Nuevo León, Mexico) at 4 °C until analysis.

The oil from each treatment was conditioned according to the methodology described by AOAC [13] and Christie [14]. A total of 50 to 100 mg of oil was placed in tubes with Bakelite caps, and 2 mL of a 2.3% methanolic potassium hydroxide solution (J. T. Baker, Madrid, Spain) was added. Subsequently, the tubes were placed in a water bath for 10 min at 75 °C and vigorously shaken at 2 min intervals until a single phase was formed. The samples were allowed to cool to room temperature, and 1 mL of boron trifluoride methanol solution (BF3) (Sigma-Aldrich, St. Louis, MI, USA) and one drop of concentrated sulfuric acid (H₂SO₄) (J. T. Baker, Madrid, Spain) were added. The mixture in the tubes was heated again to 75 °C for 10 min with gradual agitation. Afterward, the solution was transferred to polypropylene tubes, 5 mL of hexane (J. T. Baker, Madrid, Spain) was added, and the mixture was vortexed until phase separation occurred. Phase separation typically occurred within 2 to 3 min of vortexing. The organic phase (upper phase) was extracted and transferred to another polypropylene tube containing 0.5 g of anhydrous sodium sulfate (J. T. Baker, Madrid, Spain) and 0.1 g of activated carbon. The organic phase was decanted, filtered using a 0.45 μm acrodisc, and stored at −20 °C until injection into the gas chromatograph. Prior to chromatographic injection, the samples were diluted at a 1:15 ratio in BF3 (Sigma-Aldrich, St. Louis, MI, USA). For fatty acid identification, the FAME Mix C4-C24 18919 SUPELCO standard (Sigma-Aldrich, St. Louis, MI, USA) was used at a 1:30 dilution.

The chromatographic analysis of the fatty acid profile was performed according to a methodology described elsewhere [14], with some modifications. The assay was conducted using a gas chromatograph (Agilent, HP6890, Santa Clara, CA, USA) equipped with an FID detector, an automatic injector, and a SUPELCO SP-2660 chromatographic column (100 m × 0.25 mm × 0.2 μm, Sigma-Aldrich, St. Louis, MI, USA). The injection temperature was set at 250 °C, with a split ratio of 1:10, and the detector was set at 260 °C. The oven temperature program started at 140 °C for 2.95 min, then increased from 140 °C to 210 °C at a rate of 3 °C/min (over 23.33 min), and subsequently increased from 210 °C to 235 °C at a rate of 0.7 °C/min (over 35.71 min). The total runtime was 62 min.

2.4. Experimental Design

The experimental design consisted of evaluating the effect of four treatments applied to cachichín seeds: raw seeds (T1), boiled seeds (T2), seeds with commercial toasting (T3), and seeds subjected to controlled toasting (T4). A completely randomized design with three replicates per treatment was used. The response variables evaluated included water activity (αw), chromatic factors (L*, a*, b*, C*, H°, and ΔE), and the fatty acid profile. Since the results of most variables did not show a normal distribution, non-parametric statistical analyses were employed, including the Kruskal–Wallis test to identify significant differences and Dunn’s test as a post-hoc test for specific comparisons. However, for the color difference variable (ΔE), the data met the assumptions of normality and homogeneity of variances, so a one-way analysis of variance (ANOVA) was performed, followed by Tukey’s HSD test for post-hoc comparisons. A significance level of α = 0.05 was used. This approach allowed for the determination of the impact of each treatment on the physicochemical properties of the seeds.

3. Results and Discussions

3.1. Water Activity

The evaluated treatments showed a statistically significant effect on water activity (αw), as shown in Figure 2. Water activity increased notably in T2 compared to T1, while in T3 and T4, this variable decreased significantly. On the other hand, it was observed that T2 and T4 showed significant differences, confirming that the type of toasting has a major impact on reducing water activity compared to the boiling process [15]. These results highlight the ability of toasting to reduce αw, which could be related to the intensity of the heat applied and the evaporation of water during the process [16]. In other words, the degree of toasting of cachichín seeds directly influences moisture retention and the release of free water. Previous studies emphasize that the toasting process reduces αw due to the greater loss of free water during exposure to high temperatures [17]. Bagheri et al. [18] reported that the reduction in moisture content of peanut kernels (Arachis hypogaea L.) after toasting led to a less hard and crunchier texture. In the case of cachichín, the seeds from T3 and T4 exhibited a crunchy texture compared to T2, which presented a gummy texture to the touch (Figure 1). The reduction in αw suggests that the toasting process provides better stability for the seeds during storage, although it could also affect sensory perception in terms of flavor.

3.2. Color

On the other hand, the color analysis showed significant differences between treatments for L*, a*, C*, and H°, as shown in

Table 1. Color characterization (CIE Lab*) in cachichín seed (Oecopetalum mexicanum Greenm. & C.H. Thomps.) in a raw state and under applied thermal treatments.

Variable	Treatment
	T1	T2	T3	T4
L*	64.57 ± 0.11 a	55.33 ± 0.10 ab	54.90 ± 0.16 ab	47.06 ± 0.25 b
a*	5.10 ± 0.08 b	11.64 ± 0.12 a	11.10 ± 0.09 a	11.64 ± 0.01 ab
b*	20.28 ± 0.04 a	21.50 ± 0.02 a	22.12 ± 0.81 a	21.09 ± 0.07 a
C*	20.87 ± 0.05 c	23.51 ± 0.07 ab	24.46 ± 0.18 a	24.85 ± 0.06 bc
H°	75.84 ± 0.20 a	61.58 ± 0.23 b	63.30 ± 0.39 ab	63.79 ± 0.10 ab

Medians ± SE with different letters in the same row indicate a significant statistical difference (Dunn’s test, p ≤ 0.05). Notes: T1: raw seed; T2: boiled seed; T3: commercially toasted seed; T4: controlled toasted seed.

. The color index b* (p = 0.1834) did not show any significant differences due to the treatment effect. For L*, T1 presented a median of 64.62, which was higher than T2 and T3 but significantly different from T4. Conversely, an inversely proportional behavior was observed in the color index a*, where T2 and T3 showed the highest values compared to T1. Regarding C* values, T2 and T3 recorded the highest medians relative to T1. Meanwhile, the hue angle (H°) in T1 registered a higher median compared to T3 and T4 but was significantly different from T2.

Color is a key sensory attribute that influences consumer acceptance of a food product [19]. In this study, heat treatment significantly affected the color coordinates L* (lightness), a* (red-green axis), chroma (C*), and the hue angle (H°) (Table 1). It was observed that T4 showed a significant decrease in L* compared to T1, while T2 and T3 exhibited a significant increase in the a* color index. This indicates a darkening of the product, a phenomenon resulting from the Maillard reaction and sugar caramelization, which increases brown tones due to the formation of melanoidins [20]. This browning is typical of foods subjected to toasting. A study conducted on cashew nuts (Anacardium occidentale) reported a decrease in L* values and an increase in the red component (a*) due to the formation of brown pigments [21].

T2 and T3 showed a significant increase in C* compared to T1; as shown in Table 1, an increase in the chromatic intensity of the cachichín seed is evident. Specifically, it has been observed that the increase or decrease in water absorption depends directly on the heat treatment applied, which is closely related to chromatic intensity [22]. This occurs because, as water evaporates due to the effect of temperature, a series of biochemical processes are triggered, such as the Maillard reaction, which leads to the formation of melanoidins [23]. These compounds not only influence flavor and aroma but also produce visible changes in color, which tends to become warmer and more saturated [24]. This is reflected in ΔE, as T4 caused a statistically significant change in the color of the seeds (Figure 1), evidenced by the increase in ΔE (Figure 3) compared to the other treatments. This suggests that the intensity of the heat process directly influences the visual properties of the final product, likely due to more intense chemical interactions associated with higher temperatures and longer processing times [25].

3.3. Fatty Acid Analysis

The fatty acid profile in the cachichín seed shows significant differences between T1 and T3, with the first treatment consistently presenting a higher concentration of fatty acids, as shown in

Table 2. Fatty acid profile in cachichín seed (Oecopetalum mexicanum Greenm. & C. H. Thomps) under different thermal treatments.

	Treatment
	T1	T2	T3	T4
Fatty Acid	g 100 g Seed−1
Oleic acid	2.42 ± 0.04 a	1.66 ± 0.02 ab	1.44 ± 0.02 b	2.03 ± 0.03 ab
Linoleic acid	13.06 ± 0.07 a	9.08 ± 0.07 ab	6.78 ± 0.03 b	10.95 ± 0.04 ab
Linolenic acid	1.73 ± 0.03 a	1.04 ± 0.02 ab	0.75 ± 0.01 b	1.44 ± 0.02 ab
Palmitic acid	5.07 ± 0.03 a	3.52 ± 0.03 ab	3.32 ± 001 b	4.24 ± 0.01 ab
Stearic acid	2.50 ± 0.05 a	1.77 ± 0.02 ab	1.48 ± 0.02 b	1.95 ± 0.03 ab

Medians ± SE with different letters in the same row indicate a significant statistical difference (Dunn’s test, p ≤ 0.05). Notes: T1: raw seed; T2: boiled seed; T3: commercially toasted seed; T4: controlled toasted seed.

. More specifically, the unsaturated fatty acids, such as oleic, linoleic, and linolenic acids, are found in significantly higher concentrations. In contrast, T3 records the lowest concentration. This behavior suggests that uncontrolled thermal processing, such as T3, negatively affects the preservation of these fatty acids, significantly reducing their presence compared to T1. In contrast, T2 and T4 showed intermediate values, with no significant differences compared to the other treatments. Therefore, the raw cachichín seed retains its essential fatty acids, while commercial toasting without temperature and time control results in a greater loss of these compounds.

These results demonstrate the effect of thermal treatment on the nutritional value of the cachichín seed. In this study, a significant reduction in the concentration of fatty acids was observed in T3, specifically affecting unsaturated fatty acids of physiological relevance such as oleic acid (ω-9), linoleic acid (ω-6), and linolenic acid (ω-3), compared to T1. This phenomenon is directly related to the mechanism of lipid oxidation and decomposition induced by heat, which is one of the main factors affecting the stability and composition of fatty acids in foods subjected to thermal processing; these processes form lipid oxidation products (LOPs) [26].

Lipid oxidation is a natural biochemical process that occurs during the lifespan of a food product involving the reaction of fatty acids, primarily unsaturated ones [27]. In the presence of oxygen, lipids undergo an auto-oxidation reaction, generating primary lipid oxidation products (peroxides) and secondary products (aldehydes, ketones, and carboxylic acids), which significantly contribute to food deterioration [28]. However, when lipids are subjected to thermal treatments, such as toasting or boiling, the oxidation process accelerates considerably, as the addition of heat strongly induces it [29]. During the initiation phase, heat forms free radicals from the double bonds present in unsaturated fatty acids. This is followed by the propagation phase, where radicals react with oxygen to form hydroperoxides. Finally, in the termination phase, hydroperoxides decompose into volatile compounds responsible for the deterioration of food quality and nutritional value [30].

This process is particularly destructive to polyunsaturated fatty acids, such as linoleic acid (LA), which is highly susceptible to oxidation, generating volatile products like 4-hydroxy-2-nonenal (4-HNE), an aldehyde resulting from oxidation [31]. 4-HNE is a toxic compound that can have significant adverse effects on health, contributing to a variety of inflammatory, degenerative, and cancerous diseases. Its formation in oils during heating highlights the importance of selecting oils with a lower risk of oxidation and HNE formation [31,32].

In the present study, oleic, linoleic, and linolenic acid levels decreased significantly in T3, which aligns with previous studies indicating that unsaturated fatty acids are the most vulnerable to heat and prolonged contact with oxygen during thermal processing [10]. Studies suggest that the higher the temperature and the longer the treatment duration, the greater the degree of lipid saturation. Zhuang et al. [29] demonstrated that the rate of lipid saturation increases exponentially as the temperature rises from 100 to 200 °C, leading to a rapid decrease in polyunsaturated fatty acids. In the case of cachichín, T4 at 134 °C for 25 min showed a lesser impact compared to commercial toasting, suggesting that the precise control of thermal conditions could mitigate the loss of essential fatty acids.

Based on the results obtained [33], it is important to highlight the need to carefully select the thermal processing method that preserves the nutritional and sensory properties of the cachichín seed. The impact of heat on the oxidation and saturation of unsaturated fatty acids is a critical factor that must be considered when determining the optimal cooking method, as it affects both the nutritional quality and the stability of the product. These findings not only contribute to the scientific understanding of the behavior of the cachichín seed under thermal treatments but also provide a foundation for improving the processing of traditional food products in terms of shelf life, texture, and bioactive properties.

4. Conclusions

The present study demonstrated that thermal treatments applied to the cachichín seed (Oecopetalum mexicanum) significantly influence its water activity, color, and fatty acid profile. In particular, commercial toasting resulted in a greater loss of unsaturated fatty acids, while controlled toasting preserved a higher proportion of these compounds. Additionally, it was observed that water activity decreased with toasting, which could suggest improved seed stability during storage. Changes in color parameters, especially the reduction in lightness and the increase in red tones, indicate that thermal treatments affect visual appearance, which has implications for consumer acceptance. Therefore, measuring these factors can provide insights that impact seed quality, with an emphasis on the toasting process. These factors have important implications for selecting the processing method, influencing product choice depending on the desired sensory characteristics (texture, flavor) or their impact on health, nutrition, or shelf-life extension.