Impact of Conventional Pasteurization, High Temperature Short Time, Ultra-High Temperature, and Storage Time on Physicochemical Characteristics, Bioactive Compounds, Antioxidant Activity, and Microbiological Quality of Fruit Nectars

Berries are a valuable source of numerous bioactive compounds, and they have an interesting organoleptic profile. Unfortunately, their low storage life determines the need for their preservation. Among the various methods used in this regard, it was decided to use the High Temperature Short Time (HTST) (90 degrees C/15 s) and Ultra-High Temperature (UHT) (130 degrees C/5 s) methods to preserve the produced fruit nectar blends (strawberry-blackcurrant and strawberry-chokeberry). For comparison, the nectars were also preserved using conventional pasteurization (90 degrees C/10 min). Physicochemical, chromatographic, and microbiological determinations were carried out in the tested nectars before and immediately after processing, as well as after 1, 2, 3, 4, and 6 months of refrigerated storage. All methods allowed for the significant inactivation of selected microbial groups. Non-significant changes were observed as a result of HTST and UHT processing in the context of pH, TSS, and titratable acidity. Varied major changes occurred in the content of bioactive components (TPC-decrease or increase by 2-4%, TAC-decrease by 3-20%, vitamin C-decrease by 15-78%), antioxidant activity (decrease or increase by 3-9%), and nephelometric turbidity (decrease or increase by 11-65%). Both nectars showed better quality and nutritional value after the HTST and UHT processes compared to treatment with classic pasteurization. Storage affected the degradation of bioactive compounds, reduced antioxidant activity, increased turbidity, and caused the brightening of samples together with reducing redness and yellowness. Considering the results obtained, it is reasonable to recommend the use of the HTST and UHT methods in industrial conditions for the preservation of liquid fruit and vegetable products such as juices, nectars, and beverages.