Consumer evaluation of products
Results of consumer evaluation of smoothies are presented in Table 2A,B.
Table 2. (A) Consumer evaluation of apple and quince smoothies. (B) Consumer evaluation of chokeberry and black currant smoothies
|1||6.75 ± 1.91||7.50 ± 1.60||5.63 ± 1.77||5.50 ± 2.14||6.34|
|1′||6.38 ± 2.07||7.00 ± 1.41||6.88 ± 1.55||5.13 ± 2.03||6.34|
|2||6.88 ± 2.03||6.75 ± 2.43||6.00 ± 1.85||5.88 ± 1.55||6.38|
|2′||7.00 ± 2.07||6.75 ± 1.83||6.13 ± 2.30||5.75 ± 1.67||6.41|
|3||7.50 ± 1.51||6.75 ± 2.25||6.13 ± 2.59||6.75 ± 2.55||6.78|
|3′||8.13 ± 1.46||6.75 ± 1.91||7.00 ± 2.62||7.00 ± 2.56||7.22|
|4||7.50 ± 2.67||6.75 ± 2.71||6.88 ± 2.75||6.13 ± 2.64||6.81|
|4′||4.88 ± 2.30||6.38 ± 2.45||6.88 ± 2.80||5.13 ± 3.14||5.81|
|1||6.25 ± 2.71||5.88 ± 2.30||3.25 ± 1.83||5.13 ± 2.23||5.13|
|1′||5.25 ± 2.49||6.25 ± 2.12||4.50 ± 2.20||5.13 ± 2.42||5.28|
|2||6.38 ± 2.62||6.63 ± 1.60||4.00 ± 1.85||5.25 ± 2.71||5.56|
|2′||7.00 ± 2.67||6.50 ± 1.41||4.50 ± 2.56||5.13 ± 2.75||5.78|
|3||7.74 ± 2.05||7.75 ± 1.28||4.25 ± 1.39||6.13 ± 1.81||6.46|
|3′||7.63 ± 2.39||7.63 ± 1.19||4.75 ± 2.12||5.88 ± 2.03||6.47|
|4||7.50 ± 2.73||8.13 ± 1.13||6.63 ± 2.26||6.88 ± 1.81||7.28|
|4′||5.50 ± 2.45||7.00 ± 2.33||6.50 ± 2.45||6.88 ± 1.96||6.47|
|Black currant (B)|
|1||6.63 ± 2.13||4.63 ± 2.13||2.75 ± 1.67||3.88 ± 1.36||4.47|
|1′||6.75 ± 1.16||3.63 ± 2.26||2.25 ± 1.58||3.38 ± 2.00||4.00|
|2||5.75 ± 1.04||4.50 ± 2.67||2.75 ± 1.58||4.00 ± 1.93||4.25|
|2′||5.75 ± 1.39||4.25 ± 2.82||2.88 ± 1.64||3.75 ± 2.49||4.16|
|3||7.00 ± 1.31||5.88 ± 2.23||3.50 ± 2.07||5.13 ± 1.73||5.38|
|3′||6.38 ± 1.30||5.00 ± 2.56||4.00 ± 2.51||4.38 ± 1.60||4.94|
|4||6.63 ± 0.92||4.88 ± 2.80||3.25 ± 2.92||4.25 ± 2.12||4.75|
|4′||6.75 ± 1.04||5.38 ± 2.72||4.25 ± 3.01||4.38 ± 2.39||5.19|
|1||6.88 ± 1.55||3.88 ± 2.10||3.50 ± 2.88||5.38 ± 1.41||4.91|
|1′||6.50 ± 1.41||4.13 ± 1.73||3.50 ± 2.56||4.13 ± 2.64||4.56|
|2||6.75 ± 1.16||5.00 ± 1.69||3.88 ± 2.30||5.00 ± 2.33||5.16|
|2′||6.50 ± 1.20||5.00 ± 2.00||4.63 ± 2.26||4.88 ± 2.30||5.25|
|3||6.25 ± 1.91||7.25 ± 1.04||5.38 ± 1.77||6.38 ± 1.30||6.31|
|3′||6.75 ± 1.49||6.38 ± 2.07||5.75 ± 2.38||6.13 ± 1.36||6.25|
|4||7.38 ± 1.41||7.13 ± 1.64||5.63 ± 1.51||5.00 ± 1.93||6.28|
|4′||6.80 ± 1.13||6.38 ± 2.33||5.38 ± 2.33||5.25 ± 2.05||5.97|
Higher notes were given in the consumer evaluation to the smoothies based on juices from pome fruits – apples (A) and quince (Q) than to those based on chokeberry (C) and black currant (B) juices. In turn, irrespective of product variant (A, Q, C and B), consumers indicated smoothies with the addition of cranberry and black currant puree (3 and 3′) and those with the addition of bilberry puree and cloud dog rose juice (4 and 4′) as more attractive. Definitely unacceptable turned out to be the smoothies enriched with puree from Japanese quince (1–1′) and sea buckthorn (2–2′). Even a small contribution of these fruits deteriorated flavour values of the smoothies, which had a negative effect on their overall sensory desirability. The unbeneficial effect of flowering quince and buckthorn on the taste of the samples was observed especially in the products based on chokeberry (C) and black currant (B) juices. It is common knowledge that berries of both black currant and chokeberry are characterised by specific flavour bouquet. Astringency of chokeberry fruits and high acidity of black currant fruits are sometimes not acceptable to consumers, especially if these berries are the basic component of processed products. The addition of puree from flowering quince and buckthorn was additionally intensifying the sour taste of the smoothies. These fruits are known for their high content of organic acids. Titratable acidity of Japanese quince juice ranges from 2.6 to 5.6 g of citric acid/100 mL (Ros et al., 2004), whereas that of buckthorn juice reaches even 6.2 g/100 mL (Yang, 2009). It is therefore possible that this quality attribute disturbed the perception of the remaining traits of the smoothies. According to Nadolna & Szponar (1998), the proportion of sweet and sour taste plays a significant role in the sensory assessment of foods. Smoothies Q1′ (containing 40 g of quince and 10 g of sea buckthorn puree), Q2 (25 g of dog rose and 25 g of Japanese quince puree) and Q2′ (40 g of dog rose and 10 g of Japanese quince puree), that were based on quince juice (100 g/150 g of product), received higher notes in consumer evaluation than their black currant counterparts (B1, B2 and B2′). Considering differences in the production technology of juices, but also in the structure of fruits themselves, it could be expected that no other but black currant-based smoothies would be characterised by more desirable consistency. The juice from quince contains a higher number of easily sedimenting particles than the black currant juice produced via enzymatic processing. Quince fruits are harder, and their parenchyma contains a significant number of sclerenchyma cells. They are also characterised by a specific, untypical aroma and astringent taste (Wojdyło, 2011). In spite of that, consumers were rather preferring the products based on quince than those based on black currant. It was noticed, however, that in ‘B’-type smoothies, the acceptance of consumers was linked with the intensity of black currant aroma and with perceptibility of black currant taste. The products with the highest contribution of black currant (B3) received the highest sensory notes. This dependency was also confirmed by Łysoniewska et al. (2011). In turn, Nadolna & Szponar (1998) and Reguła (2009) demonstrated that the quality of processed products from black currant fruits (beverages, nectars, juices) was affected, to the greatest extent, by the taste and aroma of black currant, as the most typical and identifiable with these fruits.
The proportions between contents of main and supplementary components of smoothies affected results of their organoleptic assessment to a various extent. Although the consumers were precise in indicating their preferences of fruit species choice (cranberry, black currant, bilberry, dog rose), they were not unanimous in determining the contribution of particular smoothies components. Amongst the smoothies based on quince juice (Q) and black currant juice (B), consumers appreciated those that contained equal proportions (25 g/150 g of product) of cranberry and black currant puree (Q3, B3) as well as bilberry puree and dog rose juice (Q4, B4). The apple smoothies (A) were the most appreciated by the consumers when the contribution of black currant puree reached 40 g/150 g of smoothies (A3′). A more preferable composition of the smoothies containing dog rose juice (25 g) and bilberry puree (25 g) was indicated for the A4 sample. In turn, the chokeberry smoothies were receiving higher notes in consumer evaluation when having equal contents of cranberry and black currant puree (C3). A higher content of dog rose juice (40 g) compared with the bilberry puree (10 g) had also a positive impact on smoothies acceptability (C4′).
Contents of polyphenols and antioxidative activity of smoothies
The products selected by the sensory panel in consumer evaluation were compared in terms of the total content and profile of polyphenolic compounds (Fig. 1). The samples were analysed, by means of the liquid chromatography technique, for contents of polymers of proanthocyanidins (PA), phenolic acids (FA), flavonols (F) and anthocyanins (A). The highest content of polyphenols was determined in the smoothies based on berry fruit juices: chokeberry (442.40 mg/100 g on average) and black currant (263.02 mg/100 g on average). Compounds with a structure of polymerised proanthocyanidins were found to predominate in most of the products, except for the black currant smoothies (B3) where the main group of polyphenols were anthocyanins. The content of proanthocyanidins was higher in the smoothies containing dog rose juice, with the highest content of these compounds determined in the sample C4′ (351.46 mg/100 g). Dog rose is a valuable source of nonhydrolysing tannins, including tetra- and trimers with the structure of aglycones, mono- and diglycosides (Salminem et al., 2005). Also, chokeberry fruits are characterised by a high concentration of PA. Over 80% of proanthocyanidins identified in chokeberry fruits have a polymeric structure, whereas the remaining 20% are represented by tannins with a lower molecular mass, composed mainly of three to nine flavanol units (Gu et al., 2004).
In the analysed smoothies, the content of phenolic acids ranged from 5.19 mg/100 g (apple smoothies A3′) to 78.46 mg/100 g (chokeberry smoothies C3). In a study on berry fruits, Mattila et al. (2006) demonstrated that chokeberry was a valuable source of phenolic acids (96 mg/100 g). A higher content of these compounds was noted only in rowanberries. The smoothies with the addition of dog rose juice and bilberry puree were, generally, more rich in the investigated phenolic compounds. Only in the case of chokeberry smoothies was the content of phenolic acids significantly higher in the sample containing cranberry and black currant puree (C3). The phenolic acids profile of mixed fruit products results mainly from the specific chemical composition of fruits they were made of. In view of the results achieved in this study, it may be concluded that the type of base juice applied was the factor that differentiated phenolic compounds abundance in the smoothies.
In the analysed smoothies, the least numerous, in terms of content, group of polyphenols were flavonols. When flavonols content in smoothies was considered as affected by the type of base juice, the highest values were determined in those based on black currant (22.99 and 22.06 mg/100 g in samples B3 and B4, respectively). The smoothies with the addition of cranberry and black currant puree (variant 3 or 3′) were characterised by a higher content of these compounds than those with dog rose juice and bilberry puree (4 or 4′). A high concentration of flavonols in fruits of black currant and cranberry distinguishes them from other berry species, including raspberries, red currant (Borges et al., 2010), strawberries, chokeberry and bilberry (Häkkinen, 2000). Fruit composition of the smoothies affected also the content of anthocyanins which ranged from 8.66% (Q4) to 45.26% (B3) of the total polyphenols. A higher content of the red pigments was found mainly in the smoothies with the addition of bilberry puree and dog rose juice, compared with those containing cranberry and black currant puree.
The analysed products were also compared in terms of their antioxidative properties (Fig. 2). Statistically significant differences were found between the smoothies in the activity against ABTS cation radical. Simultaneously, the analysis of variance showed that their health-promoting potential was not correlated with results of their organoleptic assessment. The strongest antioxidative properties were expressed by the chokeberry smoothies (C) that were little acceptable in consumer evaluation. The apple and quince smoothies (A, Q), acknowledged by the sensory panel as the most attractive products, were characterised by even fivefold lower Trolox equivalent antioxidant capacity (TEAC) values.
Figure 2. Antioxidant activity of smoothies, measured by ABTS method (letters a–g means statistically homogenous groups, P ≤ 0.05).
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Worthy of emphasising is, however, that the antiradical potential of the analysed smoothies was higher compared with that of the commercially available ones. Müller et al. (2010) determined the antioxidative activity of 14 commercial samples of smoothies at a level of 0.34 – 1.28 mmol TE/100 g. The product characterised by the highest reactivity against ABTS (1.28 mmol TE/100 g) contained 9 different fruit and vegetable components, including, for example, apple puree (31%), carrot juice (29%), apple juice concentrate (25%) and strawberry puree (4%). The apple and quince smoothies produced under laboratory conditions contained only 3 fruit components; however, their antiradical potential was over 6.00 mmol TE/100 g (sample Q4). Simultaneously, these smoothies were receiving high notes in the organoleptic assessment. Hence, it may be concluded that smoothies may be produced not only from popular species of fruits (e.g. black currant, apples) but also from less-known fruits, including dog rose, quince or cranberry. The use of these components in appropriate proportions enabled developing a food product not only characterised by high health-promoting values, but also highly acceptable by consumers.
The correlation analysis demonstrated that the antioxidative potential of the smoothies was correlated not with the total content of polyphenols but rather with their chemical structure (Table 3). With account taken of conditions of the statistical test (theoretical r = 0.707, significance level P ≤ 0.05), it was found that these properties were attributable exclusively to polymers of proanthocyanidins (r = 0.904). It is also the explanation of the previously observed relationship between antioxidant activity in chokeberry smoothies (high TEAC values) and acceptance by consumers (low ratings). This is due to high levels of PAs in those products. Proanthocyanidins give fruits the astringency, which negative influence on taste of products. Nowadays, consumer preference still be strongly related to the overall flavour of the different mixtures than interest of potential of antioxidant activity and the polyphenol contribution.
Table 3. Correlation between phenolic content and antioxidant activity of smoothies
| ||Proanthocyanidins/ABTS||Phenolic acids/ABTS||Flavonols/ABTS||Anthocyanins/ABTS|
|r- correlation factor||0.904||0.489||0.106||0.527|
No correlation was observed between contents of anthocyanins (r = 0.527), phenolic acids (r = 0.489) and flavonols (r = 0.106) and the activity against ABTS cation radical, although it is common fact that the antioxidative potential of plants and their products is attributable to phenolic compounds, including anthocyanins.
Polyphenols content of food products allows determining their antiradical properties on condition of considering their amount, type and origin. Hence, in complex systems, attention should be paid not to the action of individual compounds but rather to the effects of the whole group of compounds and interactions between them. Investigations conducted by Hidalgo et al. (2010) showed explicitly that these reactions were not always synergistic in nature.
The issue of a correlation between the antioxidative activity and concentration of phenolic compounds in food products has been extensively addressed in literature, although conclusions were sometimes conflicting. Some scientists failed to find any correlation between content of phenols and antioxidative activity in plant extracts (Gil et al., 2002), whereas others pointed to strong correlations between them (Sun et al., 2002; Cioroi & Musat, 2007; Dodonne et al., 2009).
Content of ascorbic acid
The samples of smoothies were also analysed for the content of ascorbic acid (AA), and respective results were presented in Fig. 3. The analysed products differed significantly in the content of vitamin C, the highest content of ascorbic acid was determined in black currant smoothies B4 with the addition of dog rose juice and bilberry puree (168.98 mg/100 g on average). A similar content of AA was found in C4′ sample (chokeberry smoothies). This indicates a positive effect of Rosa canina juice addition on smoothies enrichment with vitamin C. An analogous dependency was observed in apple (A) and quince (Q) smoothies. The content of ascorbic acid in these products was twofold and fourfold higher than in, respectively, A3′ and Q3 samples without the dog rose juice. The advisability of applying natural means to fortify fruit products with vitamin C results from many reasons. The addition of AA has a positive effect on colour stabilisation in processed fruit products. It is of great significance especially in the processing of fruits with bright parenchyma susceptible to enzymatic browning, for example, apples or pears. It is also possible to use the synthetic form of vitamin C as an antioxidant in the technological process (Özoğlu & Bayındırlı, 2002; Markowski et al., 2009). However, the application of synthetic preparations of biologically active compounds should be minimised in the production of so-called biofood. Instead, contents of fruits being their natural sources, for example, pseudo-rose hip, should be increased in recipes of such food products, as they are a highly concentrated source of many compounds with health-promoting properties, AA in particular. Ercisli (2007) reports that the content of vitamin C in pseudo-rose hip varies between 727 and 943 mg/100 g, depending on species. In the case of cloudy apple juices, where product quality is indicated by the preservation of the natural, bright-cream colour, Japanese quince fruits may be used as a source of vitamin C. The content of AA in Japanese quince juice may reach even 112 mg/100 mL (Ros et al., 2004). Another advantage of processed products from both mentioned species is their similar colour.
Figure 3. Ascorbic acid content (mg/100 g fw) in apple, quince, chokeberry and black currant smoothies (letters A–H means statistically homogenous groups, P ≤ 0.05).
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