Fruit Pomace Powders and Pectin enhance nutritional value of Freeze-Dried Snacks -

Fruit Pomace Powders and Pectin enhance nutritional value of Freeze-Dried Snacks

This study was conducted to analyze the effect of the addition of powdered apple and blackcurrant pomace on the nutritional value, bioaccessibility of polyphenols, and antioxidant activity of freeze-dried fruit and vegetable snacks in comparison to low-methoxyl pectin as a traditional carrier agent. In this study evaluated sugars, protein, fat, ash, and total dietary fiber contents, as well as content and potential bioaccessibility of polyphenols and antiradical properties. In comparison to snacks with pectin, those with apple pomace powder were richer in carbohydrates and sugars, while snacks with blackcurrant pomace featured significantly higher protein, ash, and fat contents. The addition of blackcurrant pomace powder increased the content of potentially bioaccessible polyphenols and enhanced the antiradical properties of the products. The blackcurrant pomace exhibited a more beneficial effect on the nutritional value of the freeze-dried snacks than other carrier agents applied.

Materials and Methods

Formulations of the material consisted of 60% frozen carrot cubes, 30% orange juice, 7.5–8% water, 0.4% fresh ginger purchased at a local market in Warsaw (Poland), and 0.1% calcium lactate. Moreover, three different carrier agents differentiating the material were used. Industrial dried apple pomace powder (AP) and dried blackcurrant pomace powder (BP) were added in the amount of 2%, whereas the quantity of low-methoxyl pectin (LMP) equaled 1.5%. Each carrier agent was used separately. The mixed batches were freezedried utilizing an Alpha 1–2 LD plus freeze-dryer at a shelf temperature of 30 ◦C, chamber pressure of 63 Pa, and condenser temperature of −53 ◦C for about 48 h. The water content in the freeze-dried snacks in the sequence COG-AP, COG-BP, and COG-LMP was 1.91 ± 0.04%, 2.10 ± 0.26%, and 2.55 ± 0.11%

Sugar content was carried out using a high-pressure liquid chromatography method with refractive index detection. Protein content in the freeze-dried snacks was determined using the Kjeldahl method. The preparation of the sample consisted of material mineralization. Fat content was determined using the Soxhlet method. Determination of total dietary fiber was conducted according to AOAC 985.29 method. Ash content in the freeze-dried snacks was performed by mineralization of about 1 g of sample in a muffle furnace at a temperature of 525 ◦C.  Content of carbohydrates including sugars, specifically non-dietary fiber (non-DF) carbohydrates, was estimated as a difference remaining to 100% after subtraction of water, protein, fat, ash, and total dietary fiber contents.

The calorific value of the freeze-dried snacks was determined utilizing a pressure bomb calorimeter (own construction). Tested material in the form of 1 g pellets, prepared by grinding freeze-dried snacks into a powder and compressing it, was burned in a calorimeter chamber in the atmosphere of pure oxygen. The heat of combustion (gross calorific value) was calculated based on the change in water surrounding the chamber temperature and sample weight by dedicated software.

Polyphenol Content and Antioxidant Properties Extraction Systems: In vitro digestion was performed with standard method. First, 1 g homogenized samples were subjected to the digestion process after previous hydration in distilled water at 1:1. The first step of the enzymatic digestion was an oral phase that included adding 1.4 mL of simulated saliva stock solution (SSFESS), 0.39 mL of distilled water, 0.01 mL of 0.3 M sodium chloride, and 0.2 mL of α-amylase (1500 U/mL). Incubation of the samples was conducted in the dark, continuously shaking at 37 ◦C for 2 min. For the gastric phase, the obtained bolus was blended with 3 mL of simulated gastric stock solution (SGFESS), 0.278 mL distilled water, 0.002 mL of 0.3 M sodium chloride, 0.08 mL of 1 M hydrochloric acid, and 0.64 mL of porcine pepsin (25,000 U/mL). Then, the matrix was incubated at 37 ◦C for 120 min, as before with continuous shaking and in a dark place. The last phase, intestinal digestion, consisted of mixing gastric chyme with 4.4 mL of simulated intestinal stock solution (SIFESS), 0.524 mL distilled water, 0.06 mL of 1 M sodium hydroxide, 0.03 M of 0.3 M sodium chloride, 1 mL of aqueous bile extract (160 mM), and 2 mL of pancreatin (800 U/mL). Further incubation was performed as per the previous step, at the temperature of 37 ◦C for another 120 min, with continuous shaking and in the dark. During digestion, pH is a crucial factor for a proper course of the procedure, and it should be 7 for the oral and intestinal phases and 3 for the gastric digestion phase. Therefore, pH was controlled and corrected using 1 M sodium hydroxide and 1 M hydrochloric acid. After digestion, the samples were centrifuged (15 min, 6900× g) and the supernatants were mixed with an equal volume of methanol to stop enzyme activity.

Chemical extraction: The samples (500 mg) were extracted three times using a mixture of methanol:acetone:water (4:4:2, v/v/v), pH 5 (adjusted with 1 M HCl), ensuring high stability of low-molecular-weight antioxidants. The content of total polyphenols was determined using Folin–Ciocalteu reagent.

In order to determine antioxidant activity, 10 µL of the extracts were mixed in a 96-well plate with 250 µL of the free radical solution. The plate was shaken and incubated in a dark place for 2 h, and subsequently, absorbance of the samples were measured using a plate reader at a wavelength of 734 nm and 515 nm for the ABTS and DPPH test, respectively. The antioxidant activity was expressed as Trolox equivalents in mg Trolox/g.

Results

The addition of dried apple pomace powder made the total non-DF carbohydrate content of the freeze-dried snacks higher in comparison to other variants of the snacks, which were characterized by about 6–6.5% lower and statistically the same content. Accordingly, a similar tendency was observed in the case of glucose and fructose content, which were a few percent and significantly greater in the COG-AP sample than in COG-BP and COG-LMP, which also were similar. On the other hand, each snack’s sucrose content significantly differed and both extreme results were determined: the lowest for the freeze-dried snacks with apple pomace powder and the highest for that with blackcurrant pomace powder. As a consequence, total sugar content, including all of the investigated sugars (glucose, fructose, and sucrose), was also significantly higher in the COG-AP sample (45.76%), while for COG-BP and COG-LMP samples, it was estimated up to 43.50% and 43.77%.

The snacks with the addition of apple pomace powder contained 7.09% protein. Those with blackcurrant pomace powder contained 9.06% protein, and those with pectin, 6.64%. Statistical analysis of the obtained results indicated that the composition of samples with the addition of blackcurrant pomace (COG-BP) as a carrier agent was greater in protein content compared to the other two variants. The percentage of the protein in snacks with apple pomace powder (COG-AP) was also slightly higher than in products with lowmethoxyl pectin (COG-LMP). The results indicate that blackcurrant pomace powder used as an additive in this research was a richer source of protein than both apple pomace powder and low-methoxyl pectin.

Each type of carrier agent used in the study affected fat content in the freeze-dried fruit and vegetable snacks; its quantity was in the range of 0.64–2.04%. The lowest value was observed for the COG-LMP sample with the addition of pure hydrocolloid, and the highest was for that with blackcurrant pomace. The infusion of fruit pomace increased fat content in the obtained products.

The term ash in food products demonstrates the entire mineral residue remaining after the total disintegration of organic compounds, which usually is executed through thermal combustion. In this case, freeze-dried snacks with the addition of apple pomace powder (COG-AP) and blackcurrant pomace powder (COG-BP) were characterized by the lowest (4.81%) and the highest (7.14%) amounts of ash, respectively, and low-methoxyl pectin infusion placed the result obtained for the COG-LMP sample right in the middle (5.99%). Thus, it may be assumed that of all the carrier agents used, apple pomace contained the lowest amount of inorganic compounds, while blackcurrant pomace had the greatest. However, it must be emphasized that the composition of plant material, such as fruits and vegetables and thus their by-products, differs and fluctuates depending on variety, maturity level, as well as storage time and conditions.

Dietary fiber consists of polysaccharides, oligosaccharides and lignin that is, high molecular-weight components of edible plant structure which resist digestion and absorption in the human organism, simultaneously having a beneficial effect on the overall functioning of the digestive system and digestion process itself, as well as in the prevention of several chronic diseases.

The total dietary fiber (TDF) content in the freeze-dried snacks, which ranged from 23.90% to 24.60% and up to 29.51%. The calorific value of the freeze-dried snacks is expressed as energy of the material combustion estimated for 100 g of the product in order to match the usual form placed in food product packaging. However, the freeze-dried snacks were prepared in the shape of bars using 2 × 3 × 10.5 cm rectangular silicone molds, so one serving of the snacks was considered one bar of 10 g; thus, the approximate amount of energy delivered with the consumption of the products equals 10% of demonstrated values. According to this, the energetic values of the snacks in the sequence COG-AP, COGBP, and COG-LMP were equal to 429.46, 433.66, and 386.78 kcal/100 g of the product, and consequently, 42.95, 43.37, and 38.68 kcal per serving, respectively. The infusion of fruit pomace significantly increased the calorific value of the products by approximately 11.6% in comparison to snacks with low-methoxyl pectin (COG-LMP).

According to the data, dried apple pomace contains 36.89% total dietary fiber, 7.51% glucose, 15.96% fructose, 8.36% sucrose, 3.37% protein, 1.88% ash, and 0.38% polyphenols, vitamin C, and vitamin E combined.

The replacement of low-methoxyl pectin (COGLMP) with blackcurrant pomace powder (COG-BP) caused an increase of about 10%. The highest content of polyphenols in the potentially bioaccessible fraction (BE) was recorded in COG-BP (an increase of 44% compared to COG-LMP). Polyphenols from snacks were relatively bioaccessible—REF values ranged from 1.47 to 1.90 for COG-LMP and COG-BP, respectively. In this case, the potentially bioaccessible fractions were characterized by significantly higher activity when compared to the extracts from “chemical” extraction. The highest activity was recorded for COG-BP, while COG-AP and COG-LMP exhibited lower activity by approximately 50%. The ability to scavenge DPPH radicals was higher in the extract obtained with organic solvents than in counterparts from digestion in vitro. Compounds able to reduce DPPH radicals were poorly bioaccessible in vitro

Conclusion:

The composition of the freeze-dried carrot–orange–ginger snacks obtained with the addition of apple and blackcurrant pomace and low-methoxyl pectin as carrier agents was successfully evaluated. The replacement of pectin with apple pomace powder increased carbohydrate and sugar content, while blackcurrant pomace increased protein, ash, and fat content. The addition of blackcurrant pomace powder caused an increase in the bioaccessible fraction of polyphenols, and as a consequence, enhanced the antiradical properties of the products, thanks to the thermal stability of the anthocyanins. On the basis of the presented results, blackcurrant pomace powder may be established as having a more beneficial effect on the composition and nutritional value of the freeze-dried snacks than apple pomace powder, or even the most beneficial effect among all the applied carrier agents. The use of pomace powders as food additives may facilitate more sustainable and economically viable food processing.

Reference:

Karwacka, M., Rybak, K., Świeca, M., Galus, S. and Janowicz, M., 2022. The Effect of the Addition of Selected Fruit Pomace Powders and Pectin as Carrier Agents on the Nutritional Value of Freeze-Dried Snacks. Sustainability, 14(20), p.13012.