Characteristics of Volatile Compounds and Sensory Properties of Mixed Organic Juices Based on Kiwiberry Fruits

Abstract

Nowadays, the trend related to healthy eating is constantly growing among consumers. The juices based on kiwiberry containing over 20 vital nutrients may have a potential for usage in developing innovative products targeting health-concerned consumers. The aims of the study were: (1) to identify the volatile compounds of kiwiberry juice and its mixes with basic organic juices; (2) to determine the sensory characteristics and level of liking with regard to the tested samples and (3) to select the juice-mix with the highest sensory quality properties and liking. The measurements of volatile compounds in juices were made using a Heracles Neo ultrafast gas chromatograph (HS-GC). The sensory characteristics of the juices were assessed by Descriptive Quantitative Analysis, whereas the consumers’ overall liking was assessed on a 9-point hedonic scale. It was stated that the examined juices differed in the pattern of volatile compounds as well as in the sensory properties and the level of liking. The increasing addition of apple and pear juice to kiwiberry based juices in different ratios contributed to the exposed volatile compounds responsible for floral, sweet and fruity odours. The juice mixes with higher addition of apple or pear juices were more harmonized in terms of sensory image and represented higher levels of overall liking among consumers.

1. Introduction

Actinidia arguta, in contrast to the more popular kiwifruit (Actinidia chinensis), is known as the kiwiberry, mini kiwi, baby kiwi or hardy kiwifruit and has recently gained in popularity worldwide [1]. Compared to the common kiwifruit, kiwiberry is characterized by small, grape-size fruit with edible, thin, hairless skin, which can be easily eaten whole without peeling and producing waste. Moreover, fruit skin contains up to 15 times more antioxidants than the fruit pulp, which increases its nutritional value [2,3]. Actinidia arguta is a very promising plant thriving in various climatic zones, especially those that are too cool for growing kiwifruit. Currently, about 1600 tons of kiwiberry are annually produced worldwide, mainly in the USA, Chile, China, Australia, as well as in European countries, such as France, Belgium, the Netherlands, Austria, Switzerland, Germany, and Poland. The world area of kiwiberry cultivation and the harvest is increasing slowly but significantly [4,5,6].

Studies focused on kiwiberry have shown that this fruit contains over 20 vital nutrients. Inter alia is an excellent source of vitamin C (up to 430 mg/100 g fresh weight), minerals (K, Ca, Mg, Mn, Cu), dietary fibre, lutein, β-carotene, and chlorophylls [6,7,8]. The total phenolic content (TPC) varied from 2443.30 to 6679.18 mg/100 g dry weight, and compared to kiwifruit, the TPC was three times higher [2,7]. The main class of polyphenols are flavan-3-ols, flavonols, phenolic acids, and anthocyanins [2,9]. Thus, the fruits of kiwiberry could be an important dietary source of natural antioxidants to prevent many diseases, e.g., diabetes and cardiovascular diseases [10,11].

During the production of kiwiberry, a certain part of the fruit that does not meet the quality requirements of dessert fruit (e.g., skin damage, deformation, too ripe) can be processed into juices or jams [12]. Due to the rich chemical composition, these fruits can be a valuable source of bioactive ingredients also in preserves.

Beyond the nutritional value, the sensory characteristic of the product (colour, odour and flavour) is also the key factor influencing purchase and consumption, hence the sensory profile is a significant factor for determining the quality of juices [13].

There are various methods used to determine the sensory characteristic of juices involving humans and electronic sensors designed to mimic the sensorial abilities of humans. For volatile compounds analysis, an electronic nose system based on ultrafast gas chromatography can provide a non-invasive, rapid, sensitive and relatively low-cost test [14]. Various investigations have been performed to discriminate fruits’ and juices’ quality in both the field of scientific research and quality control [15,16,17]. However, compared with kiwifruit [18,19,20,21], the research on volatile compounds of kiwiberry is limited [22,23].

The studies on consumers perception of kiwiberry showed that consumers appreciated the sweet and aromatic flavour of the flesh together with the considerably sour taste of the skin of the kiwiberry fruits [24]. Kiwiberry based products are already consumed around the world including juices, ice creams, jams and wine but there is still a great challenge of commercialization and valorisation of these fruits [12].

Within the current consumer trend of healthy eating and drinking, juices based on kiwiberry may have a potential for usage in developing innovative products targeting health-concerned consumers. Organic consumers are a promising target for new kiwiberry juices since they are motivated to buy food by health reasons [25,26] and are prone to accept plant-based products with health enhancing properties. They are also more inclined to buy products that are low processed and have superior nutritional properties.

The kiwiberry juice is a new product concept which makes it possible to profit from the valuable properties of this fruit throughout the year. The specific sensory features of kiwiberry juice, such as the high intensity of the sour and tart taste, limit the possibilities of its consumption. The addition of other fruit juices can positively influence the sensory profile of kiwiberry juice, making it more harmonized and attractive to consumers. The offer of new juices seems to be a promising alternative in line with consumer trends relating to the growing demand for healthy as well as organic food products.

Therefore, the main purposes of the research were: (1) to identify the volatile compounds of kiwiberry juice and its mixes with organic juices, as well as (2) to determine the sensory characteristic and level of liking of tested samples and (3) to select the juice-mix with the highest sensory quality properties and liking.

2. Materials and Methods

2.1. Material

In this research, apple and pear juices (basic, well known fruits grown in Poland) and kiwiberry (a new fruit with a high content of bioactive ingredients) were used. All examined juices (not from concentrate, NFC) were naturally cloudy pressed products, freshly squeezed and pasteurized. They were packed hermetically into special sacks with cork. Kiwiberry (A. arguta) fruits were acquired from the commercial orchard in Pyzdry, Wielkopolskie Voivodeship, the western part of Poland in September 2018. The kiwiberry juice was obtained from the cultivar “Weiki” which is one of the basic A. arguta varieties grown in Europe [1]. Fruit was harvested at the harvesting maturity stage (6.5–7.5° Brix) and was stored in a cool chamber (kiwiberry is a climacteric fruit). Fruit was ripened to eating maturity stage (soft fruit, ~18° Brix) just before processing. The remaining juices used in the study, such as apple and pear juices, were also provided by an organic producer. According to the information given by the producer, organically growing fruits were harvested at the commonly used for each cultivar harvesting maturity stage. Juices were a mixture of different cultivars (respectively, apples or pears), which is a common processing practice in the industry. The organic apple and pear juices were obtained from the same producer.

The assumption of the research was to mix kiwiberry juice with other ones obtained from seasonal fruits (apple and pear) balanced in sweet and sour attributes (to avoid enhancing the intensity of, e.g., bitter taste, pungency, tart descriptors in samples). All juices were kept at a temperature of 6–8 °C until their preparation and analysis in the laboratory.

Kiwiberry juices (100% KBJ) were mixed in the following proportions with apple (APJ) and pear (PEJ) juice: 90%/10%, 80%/20%, 70%/30%; 60%/40%; 50%/50%, respectively (

Table 1. The type and proportion of juices used in the experiment.

Type of Mixture of Juices	Sample Proportions
Kiwiberry (KBJ)/	100% KBJ/	90% KBJ/	80% KBJ/	70% KBJ/	60% KBJ/	50% KBJ/
Apple (APJ)	0% APJ	10% APJ	20% APJ	30% APJ	40% APJ	50% APJ
Kiwiberry (KBJ)/	100% KBJ/	90% KBJ/	80% KBJ/	70% KBJ/	60% KBJ/	50% KBJ/
Pear (PEJ)	0% PEJ	10% PEJ	20% PEJ	30% PEJ	40% PEJ	50% PEJ

). Pure apple juice (100%) and pear juice (100%) were additionally analysed using the Heracles GC analyser. All samples of juices were prepared according to a standardized procedure.

2.2. Volatile Compounds Analysis

The measurements of volatile compounds in juices were performed using a Heracles Neo ultrafast gas chromatograph (HS-GC) (Alpha M.O.S., Toulouse, France, 2019). The instrument was equipped with a robotic autosampler system and two parallel linked capillary chromatographic columns of various polarities—MXT-5 (non-polar; 10 m × 18 µm, Restek) and MXT-1701 (slightly polar; 10 m × 18 µm, Restek)—connected to two flame ionization detectors (FIDs). The Heracles GC analyzer was coupled with a PAL-RSI autosampler to automate sampling and the injection of the gas sample. An amount of 2.0 g of juice was placed in 20 mL headspace vials and capped with a teflon/silicon rubber cap. Then, the vials were placed in HS 100 autosampler and before the headspace analysis, samples were incubated at 40 °C 300 s, while being shaken at 500 rpm. After incubation, the headspace was collected in a syringe and the injection volume on the GC was 5.0 cm³ and injection speed at 125 mL/s. Hydrogen was used as carrier gas and its flow rate was kept constant at 250 mL/s. Subsequently, a purge and trap system was used to adsorb, concentrate, and focalize the volatiles of the headspace. The temperatures of the injector and the detector (one for each column) were, respectively, at 200 and 260 °C. The analytes were divided and simultaneously transferred into the two columns. The injection on columns was carried out in three repetitions for each sample. The total acquisition time was 110 s, and the acquired signal was digitalized every 0.01 s. The method was calibrated using alkanes solution from C6 (n-hexane) to C16 (n-hexadecane) measured under the same experimental condition. The AlphaSoft v 16.0 software was used to process the data. Volatile compounds were identified on the basis of Kovats’ relative retention indices (KI) and can be connected to specific aromas that are collected in the AroChemBase v 7.0 database (Alpha M.O.S., Tuluse, France) built-in software.

2.3. Sensory Analysis

2.3.1. Sensory Profiling

The sensory characteristics of the kiwiberry juice and fruit juice mixtures based on kiwiberry were assessed using the Quantitative Descriptive Analysis method (ISO 13299:2010). Twenty-four descriptors were chosen and defined taking into account the profiling procedure. The evaluated sensory attributes were: seven odour cues (kiwiberry, apple, green, sour, sweet-nectar, refreshing, sharp), three consistency traits (density, viscidity, fruit pulp particles), eleven taste/flavour descriptors (kiwiberry, apple, green, sour, sweet, astringency, bitter, refreshing, sour aftertaste, sweet aftertaste) and three general features (harmoniousness, full-bodied and rich, overall sensory quality) of the fruit juices. The intensity of the attributes in juices was measured on a linear unstructured scale (0–10 cm) anchored at extremes “none” (on the left) to “very strong” (on the right of the scale). Overall sensory quality of the examined juices was meant as the impression of the harmony of all attributes, with no or only slight intensity of negative notes.

2.3.2. Consumer Test

In the consumer test, participants rated overall liking of the kiwiberry juice and fruit juice mixtures based on kiwiberry on a 9-point hedonic structured scale (ISO 4121:2010) ranging from “dislike extremely” (on the left) to “like extremely” (on the right side of the scale).

2.3.3. Sample Preparation and Presentation

The individual samples of juices, in amounts of 30 mL, were poured into coded 3-digit random numbers plastic containers (50 mL) and then covered with lids. The samples were presented to the panellists and consumers in random order at room temperature (21 ± 2 °C). Mineral water was used as a taste neutraliser between samples. The samples of juices were presented following a sequential monadic test [27].

2.3.4. Subjects and Testing Conditions

Ten trained assessors with over 15 years of sensory evaluation experience of various food products performed the profiling of six fruit juices (kiwiberry and its mixture with apple juice or pear juice), in two independent sessions (ISO 8586:2012). A group of 110 young adults, aged 18–21 years, took part in the consumer tests. Participants declared a regular consumption of various fruit juices, e.g., apple and multi-fruit juices, pressed juices, naturally cloudy and one-day juices.

For the profiling and the liking tests, two sets of six fruit juices (kiwiberry juice and its mixture with apple juice; kiwiberry juice and its mixture with pear juice) were evaluated. The profiling analysis of the juices were conducted during the morning and early afternoon hours, with two sessions per day of each set of products (one set × six samples × 10 assessors × 2 sessions).

The consumers tests were performed during a week for one set of six juices. The second set of six samples was evaluated after a two-week break. The same consumers carried out the assessment of each set of the fruit juices.

All evaluations were carried out in a sensory laboratory fulfilling the requirements of the ISO standard (ISO 8589:2010) for testing conditions with 10 individual testing booths and equipped with a computerised system for data acquisition (ANALSENS).

2.4. Statistical Analysis

The obtained results were statistically analyzed with XLSTATS version 2017 software by Addinsoft (Paris, France). Instrumental and sensory data were tested using variance analysis (ANOVA) followed by Tukey’s multiple comparisons, taking into account a 5% significance level.

One-way ANOVA analysis was performed to determine differences between volatile family groups of compounds of the examined juices. The results were expressed as mean ± SD of three independent experiments (n = 3). The Principal Components Analysis (PCA) was performed using the built in statistical package of the XLSTATS software to examine the similarities and differences in the profile of the volatile compounds identified in the headspace of samples.

Two-way ANOVA with interactions was used to find the differences between the juice samples in the intensity of the attributes, considering products, assessors and interactions as fixed variables (sensory profiling). One-way ANOVA was performed separately on overall liking data, considering the examined juices as a fixed source of variation. Pearson correlation coefficients were carried out to determine the relationship between mean overall liking scores and sensory attributes from profiling evaluation of the juices.

3. Results

3.1. Volatile Compounds in Kiwiberry Juice and Fruit Juices

The pattern of volatile compounds for kiwiberry and apple juice and their mixes are presented in

Table 2. Characterization of the main volatile compounds identified in the headspace of kiwiberry and apple juice and their mixes.

Chem. Family *	KI MXT-5 a	KI MXT-1701 b	Possible Matches Compounds	Sensory Descriptors **	KBJ	APJ	90KBJ/10APJ	80KBJ/20APJ	70KBJ/30APJ	60KBJ/40APJ	50KBJ/50APJ
Al	441	512	methanol	alcoholic, strong	x	x	x	x	x	x	x
A	469	665	propenal	almond, cherry	x	x	x	x	x	x	x
An	496	513	pentane	alkane	x
E	520	601	methyl acetate	ethereal, fruity		x
An	601	600	hexane	etheral		x	x	x	x	x	x
E	614	683	methyl 2-propenoate	acrid	x
Al	615	739	2-methyl-1-propanol	sweet, winey		x				x	x
Al	663	778	n-butanol	fruity, sweet		x	x		x	x	x
K	700	790	2,3-pentanedione	apple, fruity	x				x	x
An	701	778	1,2-dichloropropane	sweet				x
Al	742	853	2-methyl-1-butanol	banana, alcoholic		x		x		x	x
A	802	895	hexanal	grassy, green, fruity	x
Al	803	896	2-hexanol	fruity				x	x	x	x
E	816	896	methyl pentanoate	fruity, sweet, green		x		x	x	x	x
E	860	853	4-ethylheptane	-		x		x	x	x	x
Al	873	982	1-hexanol	floral, fruity	x	x
K	883	1086	3-mercapto-4-methyl-2-pentanone	blackcurrant					x	x	x
E	1011	1087	hexyl acetate	apple, fruity, green				x	x	x	x

* (A)—aldehyde, (Al)—alcohol, (E)—ester, (K)—ketone, (An)—alkane; ** The sensory descriptions for the listed compounds are taken from AroChemBase; ^a Kovats index for non-polar column; ^b Kovats index for slightly polar column.

and the relative content of volatile compounds in Figure 1. Based on chromatographic diagrams, seven volatile compounds were identified in kiwiberry juice, while in apple juice there were ten characteristic compounds. For kiwiberry and apple juice in different ratios, the volatile compounds varied from four (90% KBJ/10% APJ) to 11 (50% KBJ/50% APJ). With a higher proportion of kiwiberry juice, the content of volatile compounds in the tested samples decreased. These compounds were mainly alcohols, aldehydes, ketones, and esters.

The dominant compounds in kiwiberry juice were aldehydes, alkanes and alcohols followed by esters and ketones. It indicates that the propenal, hexanal, pentane and 1-hexanol, methanol are dominant substances in kiwiberry juice with the characteristic odors described as green, grassy, fruity, strong, floral, and almond-like. Furthermore, the presence of 2,3-pentanedione (ketone) and methyl 2-propenoate (ester) was observed, and the sensory descriptors for the mentioned volatile compounds were apple, fruity, and fruity, sweet, respectively. In apple juice, on the contrary, the higher content of alcohols and esters was observed, with the highest proportion of propenal, n-butanol and 1-hexanol, which contributes to the almond, fruity, sweet and floral notes. The apple juice showed also the highest concentration of esters (p < 0.05) with methyl acetate, hexyl acetate, and methyl pentanoate, which was considered to contribute to the positive aroma (fruity, sweet, green, apple). In a mixture of kiwiberry and apple juice, the presence of newly formed compounds such as 2-hexanol, 3-mercapto-4-methyl-2-pentanone and hexyl acetate was observed with the characteristic odors described as fruity, blackcurrant and apple, respectively. The kiwiberry juices with the addition of 50% APJ and 40% APJ showed the highest number of detected volatile compounds. Juice containing 50% APJ showed the highest concentration of esters and alcohols among all tested mixed juices. With the increasing concentration of kiwiberry juice in samples, the higher concentration of ketones and alkanes in the samples was identified.

Volatile organic compounds detected in kiwiberry juice, pear juice and their mixtures are listed in

Table 3. Characterization of the main volatile compounds identified in the headspace of kiwiberry and pear juice and their mixes.

Chem. Family *	KI MXT-5 a	KI MXT-1701 b	Possible Matches Compounds	Sensory Descriptors **	KBJ	APJ	90KBJ/10APJ	80KBJ/20APJ	70KBJ/30APJ	60KBJ/40APJ	50KBJ/50APJ
Al	441	512	methanol	alcoholic, strong	x	x	x	x	x	x	x
A	469	665	propenal	almond, cherry	x	x	x	x	x	x	x
Al	496	600	2-propanol	acetone, etheral		x	x	x	x	x	x
An	496	513	pentane	alkane	x
E	588	693	butane-2,3-dione	buttery, caramelized		x					x
E	614	683	methyl-2-propenoate	acrid	x		x
Ae	615	683	(Z)-1,2,-dicholoroethene	sweet		x	x	x	x	x	x
K	700	790	2,3-pentanedione	apple, fruity	x		x
A	802	895	hexanal	grassy, green, fruity	x
Al	803	896	2-hexanol	fruity, winey			x	x	x	x	x
E	815	887	ethyl methacrylate	acrid		x	x	x	x	x	x
Al	873	982	1-hexanol	fatty, floral, fruity	x
Al	859	949	(Z)-3-hexen-1-ol	floral, earthy, fresh			x	x	x	x
E	1011	1087	hexyl acetate	apple, fruity, green		x	x	x	x	x	x

* (A)—aldehyde, (Al)—alcohol, (E)—ester, (K)—ketone, (An)—alkane; ** The sensory descriptions for the listed compounds are taken from AroChemBase; ^a Kovats index for non-polar column; ^b Kovats index for slightly polar column.

, while the relative content of volatile compounds is presented in Figure 2. The conducted measurements of the pear juice (PEJ) identified the presence of seven volatile constituents that belonged to five compound categories: three esters, two alcohols, one aldehyde, and one alkene. In pear and kiwiberry juice mixes, small differences in the number of detected compounds were observed. In the mixture of kiwiberry and pear juice, the presence of newly formed compounds was observed, belonging to the alcohol compound category, mainly 2-hexanol and (Z)-3-hexen-1-ol, which contributes to fruity, earthy, floral, and fresh odor notes. The compounds 2-propanol, (Z)-1,2,-dicholoroethene, ethyl methacrylate, and hexyl acetate were detected in pear juice as well as in all tested juice mixes, regardless of the used concentration of pear juice. The volatile compounds detected in kiwiberry juice have the strongest effect on the volatile profile in sample 90PEJ (90% of kiwiberry juice and 10% of pear juice), mainly methyl 2,3-pentanedione with the apple, fruity odour, and 2-propenoate, which were found to serve as negative features to the aroma.

With the increase in the concentration of kiwiberry juice, a significant increase in the content of compounds belonging to alcohols and a decrease in the content of esters were observed (p ≤ 0.05). In pear juice, the highest content of esters was noted, with the highest proportions of hexyl acetate (45%) and ethyl methacrylate (10%), which contribute to the fruity, citrus, apple and acrid notes, respectively. The concentration of aldehydes was slightly higher in the juices with higher ratios of kiwiberry juice, but these differences were not statistically significant. Ketones were observed only in kiwiberry, pear, and 50% PEJ samples.

The Principal Component Analysis (PCA) was performed to identify groups’ components among juices based on the content of volatile composition of 13 samples (Figure 3). The first two principal components accounted for 99.47% of the total variance, where PC1 and PC2 accounted for 67.44% and 32.03% of the total variance, respectively. Discrimination of the tested samples took place mainly along the first component (PC1). The PCA allowed clear separation of the juices according to different ratios of kiwiberry juice mixed with apple and pear juice. Kiwiberry juice (KBJ) had a negative value along the horizontal and vertical axes, while apple juice sample was located in the IV quadrant, while pear juice was in the I quadrant. The kiwiberry juice mixed with apple presented smaller diversity of variation, and had negative and positive values along the horizontal axis, respectively (III and IV quadrants). Closer location of the points (samples) on the score plot suggested chromatograms similarity. The kiwiberry juices mixed with pear samples were characterized by a varying profile of volatile compounds and the samples were located in the I, II, and III quadrants, which was also confirmed by the analysis of bioactive compounds described previously.

3.2. Sensory Characteristics of the Kiwiberry Juice and Its Mixtures with Other Fruit Juices

There were statistically significant differences in intensity of many descriptors between the evaluated juices (

Table 4. Sensory profiling of the kiwiberry juice and kiwiberry/apple juice mixtures.

Attributes	KBJ	90KBJ/10APJ	80KBJ/20APJ	70KBJ/30APJ	60KBJ/40APJ	50KBJ/50APJ
o.kiwiberry	5.89 a	5.53 ab	5.29 abc	4.85 bcd	4.37 cd	4.23 d
o.apple	1.96 d	2.91 cd	2.90 cd	3.73 bc	4.65 ab	5.19 a
o.green	4.13 a	4.06 a	3.17 b	3.04 b	2.55 b	2.33 b
o.sour	3.47 a	3.26 ab	2.89 ab	2.78 ab	2.60 ab	2.37 b
o.sweet-nectar	1.34 c	2.07 abc	1.98 bc	2.55 ab	2.83 ab	3.13 a
o.refreshing	2.71 a	3.16 a	3.03 a	3.41 a	3.20 a	3.26 a
o.sharp	1.56 a	1.43 ab	1.09 abc	1.04 bc	0.83 c	1.00 bc
density	6.35 a	5.56 a	5.44 a	4.11 b	3.90 b	3.43 b
viscidity	6.91 a	6.43 ab	5.72 bc	5.46 bc	4.96 c	4.59 c
fruit pulp particles	6.33 a	5.59 b	5.35 b	5.19 b	4.34 c	3.34 d
f.kiwiberry	6.67 a	6.14 ab	5.77 ab	5.43 b	4.04 c	3.70 c
f.apple	1.15 e	2.30 d	2.73 cd	3.76 bc	4.82 ab	5.65 a
f.green	4.26 a	4.09 a	3.48 ab	3.55 ab	2.35 bc	1.97 c
t.sour	4.72 a	4.35 ab	3.96 ab	4.10 ab	3.66 ab	3.13 b
t.sweet	1.33 e	1.63 de	2.23 cd	2.64 bc	3.11 ab	3.61 a
astringency	3.10 a	2.73 ab	2.37 ab	2.58 ab	2.00 b	1.68 b
t.bitter	1.56 a	1.31 ab	0.92 ab	1.05 ab	0.66 b	0.61 b
persistent	2.11 a	1.83 ab	1.40 abc	1.79 ab	1.12 bc	0.90 c
f.refreshing	2.91 a	3.18 a	3.26 a	3.20 a	3.47 a	3.42 a
sour aftertaste	4.56 a	4.25 ab	3.75 ab	3.53 ab	3.29 ab	3.09 b
sweet aftertaste	0.79 c	1.59 b	1.70 b	2.23 b	2.22 b	3.05 a
harmoniousness	3.97 c	4.98 b	5.43 b	5.49 b	6.28 a	6.61 a
full-bodied and richness	6.74 a	6.72 a	6.42 a	6.24 a	6.25 a	6.14 a
overall sensory quality	4.58 c	5.20 bc	5.55 b	5.88 b	6.64 a	6.89 a

o.—odour; t.—taste; f.—flavour; KBJ—Kiwiberry Juice; APJ—Apple Juice; Mean values with different letters in rows are significantly different at p ≤ 0.05.

and

Table 5. Sensory profiling of the kiwiberry juice and kiwiberry/pear juice mixtures.

Attributes	KBJ	90KBJ/10PEJ	80KBJ/20PEJ	70KBJ/30PEJ	60KBJ/40PEJ	50KBJ/50PEJ
o.kiwiberry	6.17 a	5.70 b	5.34 ab	4.75 bc	4.29 c	4.22 c
o.pear	0.78 d	1.63 c	1.95 c	2.68 b	3.60 a	3.69 a
o.green	4.26 a	3.58 ab	3.29 abc	2.79 bc	2.37 c	2.14 c
o.sour	4.04 a	3.38 ab	2.77 bc	2.44 c	2.30 c	2.11 c
o.sweet-nectar	1.40 c	2.01 bc	2.10 abc	2.74 ab	3.14 ab	3.21 a
o.refreshing	3.81 a	3.17 a	3.48 a	3.41 a	3.27 a	3.03 a
o.sharp	1.90 a	1.33 b	1.35 b	1.06 bc	0.74 c	0.88 c
density	6.93 a	6.05 ab	5.33 b	4.60 c	3.9 c	3.47 c
viscidity	7.16 a	6.61 a	5.84 ab	4.92 bc	4.50 bc	4.24 c
fruit pulp particles	5.97 a	5.56 ab	5.05 bc	4.23 cd	3.94 d	3.31 d
f.kiwiberry	6.65 a	6.04 ab	5.59 bc	4.90 cd	4.34 de	3.70 e
f.pear	0.55 d	1.02 cd	1.56 bc	2.14 b	3.69 a	4.14 a
f.green	4.87 a	4.34 ab	3.79 bc	3.04 cd	2.46 d	2.37 d
t.sour	4.98 a	4.36 ab	4.04 b	3.21 c	3.09 c	2.67 c
t.sweet	1.08 d	1.17 d	1.60 cd	2.29 bc	2.91 ab	3.52 a
astringency	3.07 a	2.50 a	2.35 ab	1.39 bc	1.28 c	1.13 c
t.bitter	1.27 a	1.26 a	1.37 a	1.10 a	1.12 a	0.86 a
persistent	2.31 a	1.95 ab	2.03 ab	1.17 bc	1.14 bc	0.85 c
f.refreshing	3.53 a	2.87 a	2.98 a	3.22 a	3.25 a	3.48 a
sour aftertaste	4.16 a	3.64 a	3.55 ab	2.74 bc	2.36 c	2.35 c
sweet aftertaste	0.79 c	0.85 c	1.37 bc	1.61 b	1.65 ab	2.38 a
harmoniousness	4.30 c	4.35 c	4.93 bc	5.42 b	6.18 a	6.60 a
full-bodied and richness	7.28 a	6.53 b	5.86 bc	5.56 c	5.54 c	5.47 c
overall sensory quality	4.91 d	5.25 cd	5.51 bcd	5.81 abc	6.14 ab	6.37 a

o.—odour; t.—taste; f.—flavour; KBJ—Kiwiberry Juice; PEJ—Pear Juice; Mean values with different letters in rows are significantly different at p ≤ 0.05.

). The extent and direction of changes in sensory properties were related to the proportion of apple or pear juice to kiwiberry juice and depended on the type of attribute. The intensity of kiwiberry odour and flavour significantly decreased with the addition of apple or pear juices to kiwiberry ones, while the perception of fruit attributes like apple, pear odour and flavour significantly increased. It was found that the higher amount of apple or pear juice in the kiwiberry sample significantly decreased the sensation of green odour and flavour, as well as the intensity of sour odour and taste, in contrast to sweet taste. The proportion of sour to sweet taste was successively reduced in the evaluated samples. Similar relationships were noted for changes in the intensity of sour and sweet aftertaste. It was observed that astringency sensation was also significantly lowered while the intensity of refreshing sensation remained unchanged.

The feeling of density, viscidity and fruit pulp particles decreased with the addition of apple or pear juice to kiwiberry juice. It was stated that the feeling of harmoniousness increased significantly in kiwiberry juice mixed with apple or pear juices. The results indicated that the full-bodied and richness impression of kiwiberry and apple juice mixtures remained at a similar level in all samples, while in pear juices, they successively decreased. Furthermore, the overall sensory quality of the examined juices increased significantly with the higher ratio of apple or pear juice in kiwiberry juices.

3.3. Hedonic Liking of the Kiwiberry Juice and Its Mixtures with Other Fruit Juices

As shown in Figure 4A,B significant differences were found in consumers’ overall liking of the examined juices. The overall liking scores ranged from 4.1 to 6.8 (the kiwiberry juices and the mixture of kiwiberry juices with apple juices) and from 4.9 to 6.7 (the kiwiberry juices and the mixture of kiwiberry juices with pear juices). The increasing addition of the apple juice or the pear juice to the kiwiberry ones resulted in a significant increase in the overall liking of the samples. It was stated that consumers appreciated the following juices the most: 60% kiwiberry juice/40% apple juice, 50% kiwiberry juice/50% apple juice, as well as 70% kiwiberry juice/30% pear juice, 60% kiwiberry juice/40% pear juice and 50% kiwiberry juice/50% pear juice.

The values given in

Table 6. Pearson correlation coefficients between sensory attributes and mean hedonic liking of the juices (n = 110).

Sensory Attributes	Kiwiberry Juice, Kiwiberry/ Apple Juice Mixtures		Sensory Attributes	Kiwiberry Juice, Kiwiberry/ Pear Juice Mixtures
	Correlation	p-Values		Correlation	p-Values
o.kiwiberry	−0.954	0.003	o.kiwiberry	−0.991	0.000
o.apple	0.923	0.009	o.pear	0.974	0.001
o.green	−0.946	0.004	o.green	−0.981	0.001
o.sour	−0.955	0.003	o.sour	−0.972	0.001
o.sweet-nectar	0.932	0.007	o.sweet-nectar	0.972	0.001
o.refreshing	0.766	0.076	o.refreshing	−0.621	0.188
o.sharp	−0.974	0.001	o.sharp	−0.914	0.011
density	−0.923	0.009	density	−0.990	0.000
viscidity	−0.965	0.002	viscidity	−0.998	<0.0001
fruit pulp particles	−0.873	0.023	fruit pulp particles	−0.988	0.000
f.kiwiberry	−0.918	0.010	f.kiwiberry	−0.980	0.001
f.apple	0.940	0.005	f.pear	0.950	0.004
f.green	−0.891	0.017	f.green	−0.994	<0.0001
t.sour	−0.892	0.017	t.sour	−0.985	0.000
t.sweet	0.936	0.006	t.sweet	0.961	0.002
astringency	−0.911	0.012	astringency	−0.975	0.001
t.bitter	−0.968	0.001	t.bitter	−0.768	0.074
persistent	−0.879	0.021	persistent	−0.947	0.004
f.refreshing	0.964	0.002	f.refreshing	0.228	0.664
sour aftertaste	−0.970	0.001	sour aftertaste	−0.973	0.001
sweet aftertaste	0.888	0.018	sweet aftertaste	0.943	0.005
harmoniousness	0.970	0.001	harmoniousness	0.968	0.001
full-bodied and richness	−0.914	0.011	full-bodied and richness	−0.938	0.006
overall sensory quality	0.961	0.002	overall sensory quality	0.985	0.000

o.—odour; t.—taste; f.—flavour.

show the correlations between the sensory attributes and mean hedonic overall liking scores for the samples. It can be noted that the significant correlations were found between the hedonic liking and profiling analysis for many descriptors. Generally, the degree of liking was positively associated with apple odour and flavour, pear odour and flavour, sweet taste, harmonious sensations and overall sensory quality. The negative correlations were found for the attributes such as: kiwiberry odour and flavour, green odour and flavour, sour odour, sharp odour, consistency traits, sour taste, astringency, persistent impression, sour aftertaste, and full-bodied and richness sensation. In addition, there was a negative correlation with bitter taste and a positive correlation with refreshment flavour in the case of the kiwiberry juices with the addition of apple juice.

4. Discussion

Both the presence and the level of volatile compounds in kiwiberry juice and its juice mixes were crucial. It was found that the pattern of volatile substances influenced the sensory image of the examined samples. In juices, the diversity of sensory perceptions reported results from qualitative and quantitative perceptual interactions between odorants. According to Francis and Newton [28], the aroma is not just the sum of individual constituents, but the result of complex interactions between numerous chemical compounds. Volatile compounds can interact, showing either additive or competitive effects, which may turn even into synergistic or antagonistic effects [29]. Fruit and juice aroma can vary considerably in different fruit cultivars [30,31,32] and origins [17,33] as well as in different growing system types (organic vs. conventional) [34,35], and types of postharvest treatment and processing [36,37,38].

According to the literature, the esters, alcohols, aldehydes, ketones, and ethers are the most dominant chemical groups detected in the headspace of different apple cultivars, while in pear, esters are the major volatile components, followed by aldehydes, alcohols and ketones [39,40]. Comparable volatile compounds’ chemical groups were reported previously, which are in close agreement with our results. The aroma profile of kiwiberry juice was dominated by green and grassy aroma notes, similar to the whole fruit, as reported in previously conducted studies [22,23]. The compounds which are mainly responsible for these characteristic aroma notes is hexanal and 1-hexanol, which are formed by the enzymatic breakdown of unsaturated fatty acid during tissue disruption [41,42]. Moreover, C6 compounds (C6 aldehydes and C6 alcohols) are regarded as green leaf volatiles and contribute to the herbaceous odour in fruits [43]. This characteristic explains the sensory profile of the kiwiberry juice with an intense level of such attributes like kiwiberry odour and flavour, green odour and flavour, sour odour and taste, astringency, persistence impression and sour after taste, with low sweetness on the other hand. It was stated that the juice showed the lowest degree of liking among the samples tested.

It is worth emphasizing that methanol was observed in each tested juice sample. It was previously reported that fruit juices and related products can contain methanol at low levels. Methanol is present in pectin and is released during processing of fruits and vegetables by enzymatic activities. Possner et al. [44] presented that cloudy juices, as used in this study, have a lower amount of free methanol in comparison to clear juices, while clear juices contain a more liberated form, due to the fining and filtration using pectinolytic enzymes. Our study showed that the volatile profile of juice mixes is more complex than that in kiwiberry, pear and apple juice. In the current study, the aroma profile of juice mixes is strongly influenced by pear and apple juices’ aroma and initially detected compounds are not presented in juice mixes. These substances seem to degrade, probably due to the oxidative breakdown process [37]. Moreover, in apple juice mixes the presence of acetate ester is observed. Komthong et al. [45] associated this trend with a decrease in green aroma and an increase in sweet aroma during enzymatic browning. Hexyl acetate, the dominant ester in pear juice, was reported as possessing a strong pear-like odor [46] (Z)-3-hexen-1-ol, 1-hexanol present in pear juice mixes are typical aroma compounds found in many fruits and fruit-based products [47,48]. It was noted that the addition of apple and pear juice to kiwiberry based juices in different ratios positively influenced the sensory properties and contributed to an increase in harmonization as well as causing higher scores in overall hedonic liking.

To the best of our knowledge, the volatile components as well as the sensory characteristics of Actinidia arguta juice and its fruit mixes were investigated for the first time in the present study. The examined version of juices belong to a new product concept. The kiwiberry juice and its mixtures with other fruit juices can be an interesting alternative to the existing products, including the organic and functional ones, on the market, taking into account both sensory and health aspects. According to [49], functional beverages (products, characterized by source of physiologically active components, with beneficial properties for human health, International Food Information Council) can be produced from 100% natural juice, from concentrated juice, from nectars, or teas and named as healthy drinks. Based on the European Fruit Juice Association (AIJN) Liquid Fruit Market Report [50], the consumption of non-concentrate fruit juices has increased significantly over the last years in the European Union. It is underlined that health benefits have been recognised as a main driver for purchasing organic food by consumers [51]. The health-beneficial impacts on humans may be related to the content of, e.g., polyphenols in products. However, there are some drawbacks associated with the presence of these compounds. They may elicit undesired astringent taste in products, e.g., apple juice [52]. The sensory characteristics of the examined kiwiberry juice could also be related to the content of polyphenols that are present in large amounts in kiwiberry fruit and its peel. The mixture of fruit juices based on kiwiberry juice seems to be a reasonable approach to get more harmonious and acceptable products. The research showed that the most liked were mixed fruit juices containing: 60% kiwiberry juice/40% apple juice, 50% kiwiberry juice/50% apple juice, as well as 70% kiwiberry juice/30% pear juice, 60% kiwiberry juice/40% pear juice and 50% kiwiberry juice/50% pear juice. The other versions of the juices were, e.g., too sour and not sweet enough. According to Stolzenbach et al. [53] the basic tastes such as sweet and sour were key features and played a crucial role in liking acquisition in the case of apple juices. It was found that apple juices having a sweet/sour balance were most liked, which is in line with our results. Moreover, high flavour intensity related to sourness was stated as critical and affected liking. It was pointed out that too high and too low levels of sourness determined lower liking [53].

The key aspect in the formation of the new fruit mixes juices is: choosing the right type of fruit juice and its amount relative to the base product. Due to the fact that consumer preferences are different and may change during exposure to the product as well as taking into account the health benefits, kiwiberry juice and kiwiberry mixed juices can also be an interesting alternative to the existing juices, including organic ones. It will be important to include appropriate communication on the product packaging that will highlight its health values and information about sensory features.

5. Conclusions

Taking into account health trends and the changing preferences of consumers, it is reasonable to expand the offer of market juices, including organic ones. Kiwiberry juice, with proven health-promoting properties, can extend the range of functional juices. However, the specific sensory features of kiwiberry juice limit the possibilities of its consumption. Therefore it is desirable to mix it with other juices with more acceptable sensory features, for example, apple or pear. As shown in this study, the addition as well as apple and pear juice influenced the profile of volatile compounds in fruit juice mixtures (blends), determining the sensory properties and the degree of consumer liking. The addition of both apple and pear juice to kiwiberry juice lowered the intensity of green odour and flavour, sour odour and taste as well as astringency sensation, while the intensity of refreshing sensation remained unchanged. Feeling of harmoniousness and overall sensory quality increased in kiwiberry juice mixed with apple or pear juices. The most appreciated by consumers were juices with at least 40% apple juice and at least 30% pear juice. This can probably be explained by changes in the composition of volatile compounds responsible for the fruit, floral and sweet characteristics, which positively influenced the sensory image of kiwiberry-based fruit juice blends.