AUTHORS’ CONTRIBUTION
M. Petrović designed the work, drafted the manuscript, performed liqueur preparation and analysis of total phenolic content and antioxidant activity, and took part in sensory analysis. S. Veljović performed colour measurements, took part in antioxidant activity determination and sensory analysis and performed statistical analysis of the obtained data. N. Tomić organised and performed sensory analysis, collected the data, performed data analysis and data interpretation. S. Zlatanović took part in sample preparation and participated in sensory analysis. T. Tosti performed and described sugar and polyphenol profile analysis of the samples. P. Vukosavljević organised the raw material supply, participated in sensory analysis, its critical revision and data interpretation. S. Gorjanović planned the research, participated in the drafting of the manuscript and performed critical revision and final approval of the version to be published.
Apple juice is one of the most popular and liked beverages worldwide. Due to the increased health consciousness among consumers, beetroot and chokeberry juices have also rising consumption trends. Despite representing a considerable percentage of the processed fruit and rich source of bioactive compounds, fruit pomace, remaining after juice production, has still been underutilised. Here, the possibility of using apple, beetroot and chokeberry pomace in liqueur formulations is investigated.
Apple and chokeberry liqueurs were produced from apple and chokeberry pomace extracts, respectively. Apple/chokeberry and apple/beetroot liqueurs were obtained by combining apple pomace with chokeberry and beetroot pomace extracts in ratios 50:50 and 70:30, respectively. The sensory quality and acceptability of freshly prepared liqueurs were evaluated by experts and consumers. Sugars and phenolics were identified and quantified by high-performance anion-exchange chromatography with pulsed-amperometric detection (HPAEC-PAD) and high-performance liquid chromatography–diode array detection–tandem mass spectrometry (HPLC–DAD–MS/MS), respectively. Storability was preliminarily evaluated based on monitoring of total phenolic concentration, antioxidant activity and colour each month during 6 months of storage at 4 and 22 °C.
The expert and the consumer testing indicated that apple and chokeberry pomace could be used as raw materials without any flavour corrections while apple/beetroot pomace liqueur would require modification. High total phenolic content and antioxidant activity were found in all freshly prepared liqueurs, with chokeberry liqueur being by far superior. Among identified phenolics, ellagic acid and phlorizin were quantified as the most prominent, except in chokeberry liqueur, where phlorizin was not quantified. Despite the decrease in total phenolic concentration and antioxidant activity after 6 months, liqueurs still represented a rich source of phytochemicals. The highest phenolic compound retention and antioxidant activity maintenance were observed in chokeberry liqueur. Also, the appealing colour was retained despite the changes detected in chromatic characteristics.
The possibility of apple, beetroot and chokeberry pomace restoration into the food chain by the production of liqueurs has been demonstrated for the first time. Functional and sensorial properties of newly developed liqueurs indicated that the selected pomace represents the promising raw material for liqueur production. The applied approach represents a contribution to the circular economy in juice production.
One of the most promising waste materials from the food industry is pomace, a by-product in juice production, which mainly contains skins, pulp, seeds and stalks of the fruit. Phenolic compounds are mainly found in fruit skin as natural plant protection from environmental factors, so pomace is a valuable source of polyphenols, especially if taking into account that most of the antioxidants tend to stay in the pomace rather than transfer into juice (
Apple pomace makes up to 25–35% of the processed fruit (
Beetroot is one of the ten most powerful vegetables in terms of antioxidant capacity. Beetroot juice production yields about 15–30% of beetroot pomace. Beetroot pomace obtained from different cultivars from Serbia was reported to contain ferulic, vanillic,
Black chokeberry is among the richest sources of anthocyanins responsible for various health-beneficial properties. The majority of chokeberries are used for the production of juice with extremely potent antioxidant activity (
Food waste management has become a challenging task for the food processing industry due to a growing concern about environmental issues in recent years as well as the adoption of sustainable development goals (
According to epidemiological studies, the impact of moderate consumption of alcoholic beverages on lipid metabolism and the prevention of coronary artery diseases and colon cancer is related to polyphenol compounds and antioxidant activity (
The main aim of this research is to examine the possibility of application of apple, beetroot and chokeberry pomace, both individually or in combination, in liqueur production. In that regard, sugar content, non-volatile and volatile acidity, pH and turbidity were analysed in the obtained liqueurs. Sensory quality and consumer acceptability of the freshly prepared liqueurs were also evaluated. Additionally, the composition of individual phenolic compounds in fresh products was assessed. Changes in total phenolic content, antioxidant activity and chromatic characteristics of freshly prepared liqueurs were followed during six months of storage at refrigeration and room temperature (4 and (20±2) °C respectively) to provide preliminary insight in the produced liqueur stability during storage and to elucidate appropriate storage conditions that would ensure good retention of phenolics as bioactive compounds responsible for beneficial health effects and preservation of colour, as an important aspect for the acceptance of novel products.
Folin-Ciocalteau reagent, sodium carbonate, sodium acetate trihydrate, acetic acid, hydrochloric acid, sodium hydroxide and phenolphthalein were obtained from Merck (Darmstadt, Germany), DPPH (2,2-diphenyl-1-picrylhydrazyl) from Fluka (Buchs, Switzerland), Trolox (6-hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid), 2,4,6-tripyridyl-
The company Healthy Organic (Selenča, Serbia) provided apple and beetroot pomace, while chokeberry pomace was acquired from the family farm of D. M. Perić (Belgrade, Serbia). Wet pomace, collected immediately after juice production, was dried at the industrial scale level at 55 °C using the dehydrator Solaris (NTIM Tehnology, Belgrade, Serbia) and ground in an industrial mill to produce a fine powder that is easy to preserve, store, transport and use as a food ingredient (
For the preparation of the liqueurs, a traditional procedure involving a pilot-scale maceration was used, including two blending tanks with agitation systems (30 L), located at the experimental farm Radmilovac (Faculty of Agriculture, University of Belgrade, Serbia). In the first tank, powdered pomace was macerated in a water-alcohol mixture (
The turbidity of the analysed liqueurs was determined with a portable turbidimeter (model 2100Q; Hach, Loveland, CO, USA). The results of turbidity measurement are expressed as formazin turbidity with a reading range between 0 and 1000 nephelometric turbidity units (NTU). Non-volatile and volatile acidity (g/L) were determined according to AOAC method 945.08 (
The liqueurs were filtered through 0.22-µm filter and the filtrate was analysed using the HPAEC-PAD technique on an ISC 3000 DP liquid chromatograph (Dionex, Sunnyvale, CA, USA) equipped with a quaternary gradient pump (Dionex, Sunnyvale, CA, USA) according to the procedure reported by Vasić
The sensory quality of the freshly prepared liqueur samples was assessed in the sensory testing laboratory by a 6-member panel (35-60 years old; 4 male and 2 female) consisting of staff members from the Faculty of Agriculture, University of Belgrade, Serbia, experienced in alcoholic beverage quality judging. The samples were labelled with random 3-digit codes and presented to the panellists monadically in random order. Low sodium bottled water was used for palate cleansing. Overall sensory quality was assessed by evaluating five selected sensory characteristics: colour, clarity, distinction, odour (orthonasal olfaction) and flavour, which were rated using category scales with score ranges 0-1, 0-1, 0-2, 0-6 and 0-10, respectively. The quality of the beverages was rated as follows: excellent quality (quality score>18), very good quality (16-18), good quality (14-16), poor/unsatisfactory quality (12-14) and very poor quality (score≤12). The overall quality score, with a maximum value of 20, was calculated by adding the quality scores of the five individual characteristics. The panel evaluated all of the samples once.
Consumer acceptance tests were performed in a sensory testing laboratory by 143 students (21-25 years old; 92 female and 51 male) from the Faculty of Agriculture, University of Belgrade. The students were randomly selected, provided that they were relatively frequent (at least occasional) consumers of alcoholic beverages. The samples were labelled with random 3-digit codes and presented to the consumer panel monadically in random order. Low sodium bottled water was used for palate cleansing. Overall acceptance, appearance, odour and flavour acceptance were assessed using the 9-point hedonic scale (1=dislike extremely, 5=neither like nor dislike, 9=like extremely). The just-about-right (JAR) scales (1=too little, 5=JAR, 9=too much) were used to evaluate the intensities of colour (too light/pale – JAR – too dark), sweetness (not sweet enough – JAR – too sweet), sourness (not sour enough – JAR – too sour) and alcoholic strength (too weak – JAR – too strong). In addition, 9-point attribute intensity scales were used to assess consumer perception of fullness of flavour (1=empty, 5=medium, 9=full) and distinctiveness of flavour (1=not at all, 5=medium, 9=completely characteristic).
After filtration of samples through a 0.22-µm filter, individual phenolic compounds were identified and quantified in the filtrate using a Dionex Ultimate 3000 UHPLC system equipped with a diode array detector connected to a TSQ Quantum Access Max triple quadrupole mass spectrometer (Thermo Fisher Scientific, Basel, Switzerland) with the ion source in the form of electrospray ionisation (200 °C) in the negative mode (from
The total phenolic concentration of the prepared liqueurs was determined by the Folin-Ciocalteu method described by Singleton
Colour intensity (CI) and hue (
whereas hue (
Measurements were performed on the first day (no storage) and upon each month during six months of liqueur storage at (20±2) °C in a dark place and in a refrigerator (4 °C).
The total phenolic content, antioxidant capacity, colour intensity and hue were measured in triplicate and the results are presented as mean value±standard deviation (S.D.). The data related to total phenolic content, antiradical activity (DPPH), total reducing power (FRAP), and analytical colour measurements (colour intensity and hue) were subjected to principal component analysis (PCA). PCA was performed on the unfolded data matrix which included all replicate measurements. Upon dimension reduction, when it was clear that the first extracted principal component (PC1) was sufficient enough to satisfactorily explain the variations in the data matrix, PC1 scores for samples were subjected to 3-way ANOVA (PC-ANOVA) (
Sensory quality and acceptance (hedonic and attribute intensity) data were subjected to 2-way ANOVA with samples as a fixed factor, and assessors as a random factor. Tukey's HSD test was used to separate the mean values of samples.
Mean drop analysis was performed by combining the JAR data with the overall hedonic data, as described by Rothman and Parker (
Statistical analyses were performed using SPSS Statistics v. 17.0 (
The results of physicochemical analysis (turbidity, pH, non-volatile and volatile acidity) and quantitative sugar profile of liqueurs are summarized in
Parameter | AL | CL | ACL | ABL |
---|---|---|---|---|
Turbidimetry/NTU | 240.0±1.0 | 102.6±0.9 | 229.8±4.4 | 250.4±2.1 |
pH | 3.30±0.02 | 3.60±0.02 | 3.50±0.02 | 3.72±0.02 |
Non-volatile acidity as |
2.48±0.01 | 2.84±0.03 | 2.64±0.01 | 2.80±0.01 |
Volatile acidity as |
0.32±0.02 | 0.33±0.03 | 0.32±0.02 | 0.29±0.02 |
(8±1)a | (31±3)b | (21±2)c | (13±1)d | |
(16±2)a | (24±2)b | (22±2)bc | (19±2)ac | |
(195±18)a | (148±11)b | (159±13)a | (177±16)a | |
(219±17)a | (203±11)a | (202±16)a | (208±16)a |
L=liqueur, A=apple, C=chokeberry, B=beetroot. Values with the same letter in superscript within the same row are not statistically different (α=0.05)
Herein, the obtained pH values of prepared liqueurs were between 3.30 (apple pomace liqueur) and 3.72 (apple/beetroot pomace liqueur). Corroborating the obtained results, the pH values of differently prepared apple wines, reported by Won
No marked difference was evident in the obtained values for non-volatile and volatile acids in all analysed liqueurs. The mass concentration of non-volatile malic acid ranged from 2.48 to 2.84 g/L, whereas the mass concentration of volatile acetic acid was from 0.16 to 0.33 g/L. These results are in line with the values for the total acidity of apple liqueurs (1.16-5.82 g/L) reported by Díez Marqués
As expected, the most abundant sugars in freshly prepared liqueurs detected by HPAEC-PAD technique were glucose, fructose and sucrose. Due to the significant amount of added sugar (150 g/L), the concentration of sucrose was expectedly the highest in all samples when compared to glucose and fructose. As shown in
According to the results of the sensory quality rating of the liqueurs (
Sample | Colour* |
Clarity* |
Distinction* |
Odour** |
Flavour** |
Overall score** |
---|---|---|---|---|---|---|
AL | 1 | 1 | 2 | (5.3±0.6)b | 8.0±0.4 | (17.3±0.9)ab |
CL | 1 | 1 | 2 | (5.3±0.1)b | 8.4±0.3 | (17.6±0.3)b |
ABL | 1 | 1 | 2 | (4.4±0.5)a | 8.2±0.2 | (16.6±0.7)a |
ACL | 1 | 1 | 2 | (5.3±0.5)b | 8.4±0.5 | (17.6±0.9)ab |
L=liqueur, A=apple, C=chokeberry, B=beetroot. *Values are modes (6 assessors, 1 repetition), **values are arithmetic mean±standard deviation (6 assessors, 1 repetition). Values marked with the same letter under the same type of spirit are not statistically different (α=0.05) |
The results of testing the likeability of the liqueurs are shown in
Sample | Overall acceptance* | Appearance acceptance* | Odour acceptance* | Flavour acceptance* | Fullness of flavour** | Distinctiveness of flavour** | ||
---|---|---|---|---|---|---|---|---|
AL | (6.2±2.2)b | (7.0±1.9)b | (6.6±2.0)c | (6.0±2.3)b | 6.2±1.9 | 6.2±2.3 | ||
CL | (6.1±2.3)b | (7.4±1.9)b | (6.0±2.3)b | (6.0±2.4)b | 6.3±1.9 | 6.4±2.0 | ||
ABL | (4.5±2.5)a | (6.3±2.1)a | (4.5±2.6)a | (4.3±2.7)a | 5.9±2.2 | 6.7±2.3 | ||
ACL | (6.3±2.4)b | (7.0±1.9)b | (5.9±2.3)b | (6.2±2.4)b | 6.4±2.0 | 5.9±2.3 | ||
L=liqueur, A=apple, C=chokeberry, B=beetroot. *Ratings on the 9-point hedonic scale, **ratings on the 9-point attribute intensity scale (a consumer concept).Values are arithmetic mean±standard deviation ( |
Mean drop analysis (
The mass concentration of individual phenolics in liqueurs is shown in
Phenolic compound | AL | CL | ACL | ABL |
---|---|---|---|---|
Ellagic acid | 34.8±0.3 | 293±7 | 191.2±6.0 | 128.3±0.1 |
Phlorizin | 93.26±0.04 | n.d. | 62.3±0.9 | 51.83±0.04 |
Phloretin | 10.12±0.03 | n.d. | 5.33±0.01 | 4.04±0.00 |
Quercetin | 10.5±0.0 | 19.56±0.01 | 16.79±0.04 | 14.64±0.04 |
Quercetin-3-O-galactoside | 7.66±0.03 | 9.97±0.09 | 9.6±0.1 | 8.85±0.02 |
Quercetin-3-O-rhamnoside | 4.72±0.04 | 4.79±0.06 | 4.21±0.05 | 3.76±0.03 |
Ferulic acid | 11.46±0.08 | 12.4±0.1 | 12.0±0.4 | 8.63±0.04 |
5-O-caffeoylquinic acid | 12.39±0.07 | 11.36±0.05 | 11.2±0.1 | 3.46±0.05 |
Protocatechuic acid | 4.95±0.04 | 7.1±0.1 | 7.05±0.07 | 4.35±0.01 |
5.37±0.07 | 3.75±0.01 | 3.67±0.07 | 0.023±0.00 | |
Rutin | 2.81±0.04 | 4.2±0.1 | 3.13±0.04 | 3.35±0.05 |
1.94±0.03 | 4.09±0.06 | 3.98±0.06 | 4.35±0.05 | |
Pterostilbene | 1.44±0.00 | 1.6±0.1 | 1.2±0.1 | 0.23±0.00 |
Aesculin | 0.86±0.03 | 0.69±0.03 | 0.76±0.05 | 0.74±0.05 |
Isorhamnetin-3-O-rutinoside | 0.66±0.02 | 0.86±0.03 | 0.74±0.02 | 0.60±0.03 |
Isorhamnetin | 0.38±0.00 | 0.53±0.00 | 0.45±0.02 | 0.43±0.04 |
Caffeic acid | 0.26±0.01 | 0.63±0.02 | 0.62±0.03 | 0.01±0.00 |
Naringin | 0.36±0.00 | 0.38±0.00 | 0.37±0.01 | 0.46±0.02 |
Sinapic acid | 0.23±0.01 | 0.25±0.01 | 0.24±0.01 | 0.11±0.00 |
Taxifolin | 0.26±0.01 | 0.27±0.01 | 0.29±0.00 | 0.15±0.00 |
L=liqueur, A=apple, C=chokeberry, B=beetroot, n.d.=not determined |
All produced liqueurs showed notable total phenolic content at the time of preparation, with the following descending order of activities: chokeberry>apple/chokeberry>apple>apple/beetroot liqueur (
Temperature/°C | AL | CL | ACL | ABL | |||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
no storage | (871±32)f | (3.1±0.0)h | (8.1±0.1)h | (3473±33)i | (28.0±0.7)h | (58.9±0.5)i | (2960±35)h | (16.2±0.3)h | (29.5±1.3)e | (790±8)g | (2.3±0.2)f | (9.6±0.4)g | |||||||
4 | 1 | (646±24)e | (2.8±0.0)fg | (8.5±0.1)h | (3205±42)g | (21.9±0.4)g | (51.5±1.3)g | (2177±54)g | (12.9±0.39)g | (31.6±0.4)f | (524±18)f | (1.9±0.0)e | (5.8±0.1)e | ||||||
2 | (645±9)e | (2.6±0.1)f | (7.7±0.3)g | (3218±21)g | (19.3±0.6)f | (47.9±0.4)f | (1977±18)ef | (11.34±0.2)d | (28.4±1.3)de | (482±4)e | (1.6±0.1)d | (5.0±0.1)d | |||||||
3 | (552±6)d | (2.0±0.2)e | (5.4±0.1)e | (29429±11)f | (19.6±0.2)e | (35.1±0.6)e | (1919±47)e | (12.7±0.2)fg | (23.2±0.5)c | (358±4)d | (1.2±0.0)c | (3.6±0.1)c | |||||||
4 | (409±3)c | (1.5±0.1)d | (4.0±0.1)d | (2658±26)e | (16.3±0.7)b | (27.3±0.2)b | (1579±18)c | (8.7±0.8)c | (17.6±0.1)b | (321±1)c | (0.8±0.1)b | (3.0±0.0)b | |||||||
5 | (256±2)ab | (0.9±0.0)ab | (2.9±.0.0)c | (2500±20)d | (17.6±0.6)cde | (31.8±0.2)cd | (840±17)a | (4.8±0.2)a | (9.8±0.4)a | (139.0±2.6)a | (0.7±0.2)b | (1.2±0.1)a | |||||||
6 | (226±2)a | (1.2±0.0)bc | (2.3±0.1)b | (1729±15)a | (14.4±0.3)a | (19.9±0.9)a | (784±13)a | (7.9±0.4)c | (10.3±0.1)a | (153.1±2.1)a | (0.6±0.1)ab | (1.3±0.1)a | |||||||
20 | 1 | (640±2)e | (2.9±0.0)gh | (7.6±0.1)g | (3302±33)h | (23.8±0.5)h | (54.3±0.7)h | (2228±58)g | (11.5±0.2)d | (28.1±0.8)de | (527±4)f | (2.0±0.1)e | (6.5±0.1)f | ||||||
2 | (618±6)e | (2.2±0.0)e | (6.6±0.1)f | (3400±10)i | (21.9±0.2)g | (51.8±0.8)g | (2035±13)ef | (11.8±0.5)df | (26.2±1.5)d | (484±3)e | (1.6±0.0)d | (5.0±0.0)d | |||||||
3 | (542±2)d | (2.2±0.1)e | (3.4±0.1)d | (2996±26)f | (21.0±0.5)de | (33.3±0.8)de | (1749±33)de | (11.7±0.3)df | (16.3±0.3)b | (317±1)c | (1.3±0.0)c | (3.4±0.1)bc | |||||||
4 | (424±3)c | (1.4±0.2)cd | (3.3±0.5)d | (2648±29)e | (18.5±0.5)c | (30.2±0.2)c | (1280±52)b | (6.1±0.1)b | (16.3±0.6)b | (332±5)c | (0.4±0.1)a | (3.3±0.5)bc | |||||||
5 | (255±4)ab | (0.8±0.1)ef | (1.3±0.1)ab | (2034±21)c | (14.5±0.8)a | (21.5±0.4)a | (832±42)a | (4.8±0.0)a | (8.2±0.5)a | (175±4)b | (0.5±0.0)ab | (1.3±0.1)a | |||||||
6 | (268±6)b | (0.9±0.0)a | (1.3±0.1)a | (1718±71)a | (14.6±0.2)a | (21.2±0.9)a | (874±9)a | (5.9±0.1)b | (8.0±0.3)a | (181±4)b | (0.5±0.0)ab | (1.29±0.1)a | |||||||
L=liqueur, A=apple, C=chokeberry, B=beetroot; TPC= total phenolic concentration expressed as gallic acid equivalent (GAE) per litre of liqueur. Antioxidant activity (DPPH and FRAP) expressed as Trolox equivalent per litre of liqueur. Values are arithmetic mean±standard deviation. Values marked with the same letter within the same column are not statistically different (α=0.05) |
It can be noticed that the total phenolic concentration determined by Folin-Ciocalteu assay was higher than the sum of individual phenol concentrations quantified by HPLC. This is in line with previous studies that explained such result by the interference of various substances other than phenols (organic acids, residual sugars, amino acids, proteins and other hydrophilic compounds) in the Folin-Ciocalteu assay, various responses of individual phenols, presence of only low molecular mass phenols in extracts (
A similar antioxidant activity of liqueurs measured by DPPH and FRAP assays was obtained as for total phenolic concentration, with chokeberry liqueur being by far the strongest radical scavenger ((28.0±0.7) and (58.9±0.5) mmol/L, respectively). However, in the case of results obtained by FRAP assay, it can be observed that apple/beetroot liqueur had slightly higher antioxidant potential than apple liqueur.
The results of total phenolic concentration and antioxidant capacity trends of analysed liqueurs during six months of storage at two different temperatures are presented in
In all cases, with the exception of chokeberry liqueur stored at 4 °C, there were no significant differences in total phenolic concentrations after 5 and 6 months of storage, leading to the assumption that the decomposition of phenolic compounds is complete after 5 months.
The decrease of antioxidant activity of chokeberry and apple/chokeberry liqueurs during storage, measured by DPPH, was also the least prominent (by approx. 50%) compared to apple and apple/beetroot liqueur, where drops greater than 60% were observed. At the same time, antioxidant capacity reduction determined by FRAP method was between 65-85% for all analysed liqueurs.
There is scarce literature data on the possibility of utilisation of apple, beetroot and chokeberry pomace in the production of antioxidant-rich alcoholic or non-alcoholic beverages. In a study dealing with antioxidant activity of liqueurs made from ten red fruits, in the majority of samples, the concentration of phenolic compounds decreased over the considered periods (
The majority of spirits, including liqueurs, are commonly stored safely at room temperature since alcohol provides microbiological stability. Studies on a half-year period of sour cherry liqueur storage showed that their characteristic features are almost unchanged if stored at 15 °C and without sugar added, but organoleptic properties were better in samples stored at 30 °C (
The strong correlation between total phenolic concentration and antioxidant capacity measured by DPPH and FRAP was confirmed by high correlation coefficients (0.978 and 0.966, respectively). Such a result indicates that the potent antioxidant capacity of the liqueurs is highly influenced by phenolics present in apple, beetroot and chokeberry pomace, as well as in the prepared mixtures, which corroborates the previous reports (
Colour is one of the most important quality features of liqueurs with a huge influence on consumer preferences. The determination of the optimal storage conditions can prevent colour changes that consumers associate with food spoilage and can thus be crucial in preventing economic losses, especially in sales of new products. According to literature, the intense red colour of chokeberry liqueurs depends on the structure and concentration of anthocyanins (
The colour intensity and hue of the analysed liqueurs are shown in
Temperature/°C | CI | ||||||||
---|---|---|---|---|---|---|---|---|---|
AL | CL | ACL | ABL | AL | CL | ACL | ABL | ||
no storage | 0.155e | 2.259f | 1.213h | 0.391j | 2.784e | 0.497a | 0.555a | 2.924c | |
4 | 1 | 0.137c | 1.058a | 0.671e | 0.266g | 2.871ef | 0.900d | 0.954bc | 2.202a |
2 | 0.170f | 1.162d | 0.732g | 0.327i | 3.118fg | 0.869c | 3.118g | 2.538b | |
3 | 0.094a | 1.173d | 0.688f | 0.127a | 2.440d | 0.856b | 0.877b | 3.679f | |
4 | 0.137c | 1.104c | 0.683f | 0.136b | 1.391b | 0.895d | 0.956bc | 4.957i | |
5 | 0.146d | 1.173d | 0.604d | 0.163c | 0.679a | 0.94e | 0.959bc | 4.387h | |
6 | 0.100ab | 1.061a | 0.615d | 0.161c | 3.211g | 0.960f | 1.023c | 4.191gh | |
20 | 1 | 0.131c | 1.158d | 0.607d | 0.230f | 2.562d | 0.996g | 1.075cd | 3.118cd |
2 | 0.193g | 1.224e | 0.692f | 0.296h | 3.118fg | 1.099h | 3.118g | 2.448ab | |
3 | 0.100b | 1.097bc | 0.511bf | 0.181d | 2.636de | 1.124i | 1.183de | 4.052g | |
4 | 0.166f | 1.083b | 0.490a | 0.191e | 1.750c | 1.186j | 1.310ef | 3.265de | |
5 | 0.102bd | 1.107c | 0.527c | 0.168c | 3.277g | 1.275k | 1.327f | 4.451h | |
6 | 0.206h | 1.053a | 0.520bc | 0.178d | 2.656de | 1.329l | 1.377f | 3.548ef | |
L=liqueur, A=apple, C=chokeberry, B=beetroot. Values are arithmetic means (standard deviation values of triplicates were zero or |
The colour intensity of apple/chokeberry, chokeberry and apple/beetroot liqueurs decreased throughout the evaluated storage period, although the reduction was nonlinear. No particular trend of change in CI over time can be observed for apple liqueur, at both tested temperatures. Comparing the results obtained at the two tested temperatures, it can be observed that the lower temperature did not prevent the degradation of colour during storage.
Except in the case of apple liqueur, an increase in hue was observed during the evaluated storage period, indicating the growth in the percentage of the yellow colour and/or loss of the red colour. The colour of myrtle liqueur, evaluated according to the classic spectrophotometric parameters of intensity and hue, showed marked variability during storage in the bottles with increasing headspace, while values remained almost constant in unopened ones (
The results of principal component analysis (PCA) applied to the unfolded data matrix, derived from the antioxidant activity (total phenolic concentration, FRAP and DPPH) and colour measurements (hue and CI), showed that only the first extracted principal component had an eigenvalue larger than one, and according to both the Kaiser criterion and scree plot (
The results of ANOVA applied to PC1 scores showed that antioxidant activity was significantly affected (p<0.05) by all examined factors: type of pomace used, storage time and temperature. Also, all interactions among the factors were statistically significant. The plots of factor interactions are shown in
Storage time by type of product/pomace (by storage temperature) interaction profile plots as a result of three-way ANOVA (
This trend for antioxidant activity over the storage period correlated with the level of antioxidant potential recorded for control (freshly prepared) samples. Mean PC1 scores for the samples after preparation differed significantly (p<0.05) from each other, in the same descending order as observed during the period of storage. Also, regardless of the storage temperature, the curves for chokeberry and apple/chokeberry liqueurs had slightly steeper slopes than apple and apple/beetroot liqueurs, which remained milder (
An innovative way of powdered apple, beetroot and chokeberry pomace utilisation was demonstrated. As a source of bioactive molecules, pomace was employed to obtain liqueurs with notable functional and acceptable sensorial properties. According to our knowledge, this is the first study that deals with the application of powdered pomace from industrial juice production in liqueur development. Sensorial properties of freshly produced liqueurs indicated the possibility of chokeberry and apple pomace exploitation in the production of liqueurs without flavour correction, while further research aimed at finding a way to improve sensorial properties of apple with beetroot pomace liqueur and sensory analysis of liqueurs during storage is required. Analysis of individual phenolic compounds revealed the predominance of ellagic acid and phlorizin in freshly prepared liqueurs, except in the chokeberry pomace liqueur in which phlorizin was not quantified. The high total phenolic concentration and antioxidant activity of freshly prepared liqueurs prove that apple, beetroot and chokeberry pomace can be used as a source of bioactive molecules and also indicate the potential contribution of liqueurs to bridging the antioxidant gap in the modern diet. The storability of liqueurs during the initial six months of storage, estimated based on antioxidant activity and total phenolic concentration, showed that they remained a rich source of bioactive compounds despite the significant decrease of surveyed parameters. Measurable changes in colour characteristics were also detected but the appealing colour was retained. Acceptable sensorial properties of freshly prepared liqueurs as well as notable total phenolic concentration and antioxidant activity during 6 months of storage, along with the growing market demand for natural products, indicate the developed products might be an additional source of phytochemicals. The suggested pomace application can also contribute to the adoption of circularity into the fruit and vegetable processing industry.
FUNDING
All authors declare no competing financial interest. This work was supported by the Ministry of Education, Science and Technological Development, Republic of Serbia (Grant No. 451-03-9/2021-14/ 200051).
CONFLICT OF INTEREST
The authors declare no conflict of interest.