The Influence of Flow Microwave Pasteurization Parameters and Variety of Blue Honeysuckle Berry on Selected Quality Parameters of Nectars

Continuous-flow microwave (MW) pasteurization is a relatively new and still poorly understood preservation method with great potential for industrial applications. The raw material for the research was blue honeysuckle berries (Lonicera caerulea var. kamtschatica Sevast.), which are considered a rich source of bioactive compounds. This study investigated the effects of various MW power (2100 W, 2400 W, 2700 W, 3000 W), traditional pasteurization parameters (90 °C/10 min), and blue honeysuckle berry varieties (Aurora and Indigo) on the quality of nectars after the preservation process and during 16 weeks of cold storage (4 °C). Physicochemical measurements were performed (pH, titratable acidity, total soluble solids, nephelometric turbidity), together with spectrophotometric (total polyphenol content, antioxidant activity, color parameters) and chromatographic (L-ascorbic acid, anthocyanins, phenolic acids, iridoids) analyses. A slight effect of MW power on pH, total soluble solids, total titratable acidity, turbidity, and color parameters was demonstrated. Immediately after preservation, the ∆E* values of the samples subjected to MW ranged from 0.48 to 1.06, while after PT they ranged from 1.90 to 5.83. Considering the content of bioactive components, it has been proven that the MW method is more beneficial than traditional pasteurization due to a higher retention of anthocyanins (1–6% reduction or 1–5% increase after MW or 5–16% reduction after PT—values for the individual anthocyanins) and partially higher antioxidant activity. After 16 weeks of storage, MW-treated samples contained more anthocyanins and total polyphenols than untreated samples. The study showed the negligible effect of MW processing on iridoid content; these compounds were the most stable bioactive compounds present in the preserved nectars during storage (changes of up to 5%).