Development of biscuits technology with the addition of grape pomace powders

Abstract

The thesis is dedicated to the scientific substantiation and development of the technology of biscuits enriched with biologically valuable substances due to the addition of powders from grape pomace, as well as from seeds and skin separated from pomace. Cabernet Sauvignon grapes grown in the eastern part of China were used to make the powders. The paper presents the results of an analytical review of literary sources, namely, the directions of grape pomace processing, the peculiarities of their chemical composition, the influence on the properties of gluten and starch, and on the formation of the structure of wheat dough. A study of the chemical composition of grape powders showed that their main component is dietary fiber, the content of which ranges from 59 to 68%. Only 13% of them are soluble. In seeds, fiber prevails, in skin – pectin substances. In addition to dietary fiber, pomace contains proteins (from 8.75% in the seeds to 16.31% in the skin), fats (up to 20.92%), minerals, including K, Na, Ca, and Mg, Fe, Cu, Zn, Mn, Cr, and Se. Low lead content and absence of cadmium in grape powders were noted, although Chinese national standards "Green Food – Dried Fruits" (NY/T 1041-2010) and "Green Food – Temperate Fruits" (NY/T 844-2010) allow the content of these elements in plant products at the level of Pb ≤ 1 mg/kg, Cd ≤ 0.05 mg/kg. The content of some elements differs from the literary values, which is related to the characteristics of the variety and the origin of the grapes taken for research. The qualitative and quantitative polyphenol composition of grape powders was investigated using high-pressure liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) methods. It is shown that polyphenols in grape seeds powder are represented mainly by flavonols (quercetin, morin, myricetin, etc.) and benzoic acid derivatives (vanillic, syringic, gallic acid, etc.), while the amount of 9 flavan-3-ol (catechin, epicatechin, epicatechin- gallate, epigallocatechin-gallate) and cinnamic acid derivatives is small. In grape seeds powder, approximately 80% of the non-anthocyanin polyphenols are flavan-3-ols, of which the methanolextracted ones are significantly more abundant than the benzoic acid derivatives and flavonols. Grape seeds also contain low amounts of cinnamic acid. In general, the obtained results correspond to the results of other studies, but differ from the data on the content of quercetin and isoquercetin in the seeds powder. The content of the quercetin is much lower, and of the isoquercetin is much higher, than is known from the literature. This is probably because the polyphenol composition of grape seeds depends on many factors, such as grape variety, growing climate, geographic environment, pomace fermentation time, and berry maturity. The high antioxidant capacity of grape polyphenolic compounds has been confirmed. We also confirmed that the antioxidant activity of their polyphenolic extract is significantly superior to that of vitamin C. The color of the composite flour obtained by mixing wheat flour with grape powders was studied. It is shown that all types of powders increase the dark pink spectrum of the color gamut in the mixture, and the addition of skin powder gives the samples a blue color. Thermomechanical properties of the dough and its individual components – gluten and starch – were investigated using the Mixolab. It was established that grape powders have a significant effect on the water absorption of composite flour, but the direction of the effect is different. Thus, the dough with the addition of powders from grape pomace and seeds is characterized by a lower ability to absorb moisture compared to the control sample. This result contradicts other studies, as the addition of dietary fiber usually leads to an increase in water absorption. But it can be explained by the fact that the lipids contained in these powders can partially cover starch granules and protein molecules, reducing water absorption during mixing. Grape skin powder, on the contrary, increases the water absorption of the dough. When adding 20% wt. of this powder, water absorption increases by 9.65%, which is due to the high protein content in the additive and the difference in the composition 10 of dietary fibers. Grape skin powder protein contains a large amount of alanine and lysine, which are responsible for water absorption. The resultant addition effects on the rheological and microstructural properties were studied. It has been established that grape powders increase the dough development time, stability time as well as increase its strength. The addition of the three grape powders reduced elastic modulus and viscous modulus. The study of the microstructure of the dough samples showed that the addition of grape flour breaks the integrity and continuity of the gluten in the dough. The results obtained using the rapid visco-analyzer (RVA) indicate that the addition of grape powders has a limited effect on the gelatinization temperature, slightly increasing it. In all cases, the attainment of the maximum paste temperature decreased due to an increase in gelatinization temperature. The increase in viscosity during cooling of the starch paste is due to the fact that powders from grape pomace can worsen the thermal stability and resistance of starch granules to mechanical damage. Differential scanning calorimetry (DSC) results showed that the enthalpy required for gelatinization was significantly reduced due to the relative decrease in starch content, which was consistent with the RVA results. The biscuits recipe was optimized with the addition of grape powders. It was found that biscuits with the addition of 15% grape seeds powder, 5% grape skin powder, and 10% grape pomace powder have the best quality indicators. The optimal amount of added powdered sugar was 35%, palm oil – 9%, and the ratio of baking soda:gluconolactone:ammonium bicarbonate was 0.6:0.8:1.0. Under these conditions, the biscuits had a chocolate color, a strong grape flavor, the overall acceptability of the biscuits was high, and the total microorganism and coliform counts were within the safe range. The nutritional composition and antioxidant properties of three types of biscuits under optimal conditions of the biscuits process were evaluated. The results showed that biscuits’ hardness, chewability, and fragility decrease with increasing dosage of grape powders. Biscuits with the addition of 10% grape pomace powder showed increased resistance to oxidation. 11 Analysis of the biscuits’ digestive characteristics showed that with increasing addition of grape pomace powder, the amount of rapidly digestible starch decreases, and the amount of fully digestible starch increases. Research of aromatic components in the samples of biscuits can be established that at the level of 10% of additives biscuits have a mixed taste with a taste of bitter almond, banana, herbs, toasted and nutty. Collectively, grape powders have promising potential as raw materials for biscuits enrichment. According to a first-order kinetic model of oil rancidity, the shelf life of biscuits with addition of grape pomace powders stored at 37°C, 47°C, and 57°C were 198 days, 105 days, and 77 days, respectively, and further adjusting the temperature and of the storage period made it possible to obtain the kinetic equation ln (T) = – 0.0024S + 4.2225 (R2 = 0.9412). The results of the confirmatory experiment showed that the relative error of the predicted value of the expiration date of the biscuits, obtained by calculation, is less than 10%.