No abstract

In blackcurrant juice powders made using freeze-, vacuum-, and spray-drying methods, 19 polyphenolic compounds were identified: anthocyanins (6), (+)-catechin, flavonols (8), and phenolic acids (4). The highest content of identified polyphenols was noted after vacuum drying at 90 °C, which was connected with the thermally induced release of (+)-catechin. Drying at this temperature also increased the formation of the Maillard reaction/caramelization product, hydroxymethyl-l-furfural, when inulin was added. The higher the vacuum drying temperature was, the stronger the degradation of anthocyanins was. Inulin was a better protectant of anthocyanins than maltodextrin, except during vacuum drying at 90 °C, which probably triggered inulin’s participation in the formation of hydroxymethyl-l-furfural (HMF), thus limiting its capability to protect anthocyanins. Flavonols and phenolic acids were best retained after vacuum drying at 50 °C. Carrier selection affected only slightly, whereas carrier concentration did not affect, the content of flavonols and phenolic acids. The quality of fruit juice powders should be considered taking into account a broad spectrum of factors, including the initial composition of the material subjected to drying, the drying parameters, the carrier type and concentration, and the interactions that occur during the thermal treatment of fruit juices.

Cranberry juice has a high content of polyphenols, which makes it a valuable raw material with health-promoting properties. On the other hand, the bitter and astringent taste of cranberry limits its consumption in fresh form (fruit, juice). For this reason, new formulations of cranberry products based on natural additives are sought, e.g., in the form of carriers, which not only allow the drying of liquids to form powders, but which can also affect the retention of bioactive compounds. This study aimed at the evaluation of the influence of different carriers and concentrations applied to cranberry juice and their influence on the physico-chemical properties of the powders obtained. Freeze-dried powders had approximately eight times higher moisture content than products gained after the spray-drying process. The bulk density of freeze-dried product was approximately 11% higher when compared to spray-drying. Freeze-drying and spray-drying had a similar influence on the total polyphenolic compound content and antioxidant capacity. When the concentration of carriers was concerned, it was indicated that a higher content of carrier resulted in a lower moisture content, water activity, CIE L*a*b* coordinates, total polyphenolic content, and antioxidant capacity of the powders obtained, pointing to a strong influence of the juice composition on the final properties of the powders.

The aim of this study was to determine the effect of blanching and frying on selected properties of potato crisps of yellow- and purple-fleshed cultivars. The material used was yellow flesh cv. Ismena and purple flesh cv. Provita. Potato slices were blanched (1–5 min at 80–90 °C) and then fried (155–175 °C). The control sample was comprised of crisps that were not blanched. The fat content and color parameters were determined in crisps, while in defatted samples, the following were determined: the content of total polyphenols; antioxidant capacity, measured by the ability to scavenge the ABTS•+ radical cations (TEAC ABTS) and by the FRAP method; and the level of fluorescent intermediary compounds (FICs) and browning index (BI), as indicators of the progress of the Maillard reaction. The content of kynurenic acid (KYNA) was examined in the raw material, in slices, in the water after blanching and in the crisps. Blanching affected the fat absorption, with time being more critical than temperature. The color of crisps from yellow flesh potatoes after blanching lightened, while the color in the purple samples darkened. The content of total polyphenols was higher in purple crisps. Increasing the temperature and shortening the time of blanching increased the polyphenol content and the antioxidant capacity. Blanching decreased the level of FICs, while frying increased FICs. Higher BI values characterized the crisps from cv. Provita. Blanching reduced BI values by 50%, while frying at highest temperature increased these values. The content of KYNA in purple potatoes was almost three times higher than in yellow ones. Blanching and frying decreased the KYNA content in potatoes and fried crisps.

Plum pomace, an agro-industrial waste product has received attention due to the worldwide popularity of plums. During convection, the content of flavan-3-ols decrease, except drying at 90 °C, whereas the content of i.e. chlorogenic, 3-p- and 4-p-coumaroylquinic acids, quercetin rutinoside, and galactoside was observed to increase along with the increase in process temperature. The highest content of all identified polyphenols was found in plum pomace powders obtained using a combination of convective at 90 °C and microwave vacuum drying (MVD) at 120 W, whereas the highest retention of the group consisted of phenolic acids, flavonols, and anthocyanins was noted when CD 70 °C/MVD 120 W was used, pointing to a strong influence of the type of polyphenols on their changes caused by drying. The correlations between TEAC ABTS and the sum of flavonoids (r = 0.634) and anthocyanins (r = 0.704) were established. The multiple regression analysis showed that polyphenol content was more strongly affected by drying time than by maximum temperature, whereas antioxidant capacity was more influenced by maximum temperature of sample than by drying time.