Abstract
Bilberries are a rich natural source of phenolic compounds, especially anthocyanins. The press cake obtained during the processing of bilberry juice is a potential source of phytochemicals. The objective of this study was to evaluate different drying techniques and the fractionation of bilberry press cake powder toward obtaining phenolic‐rich ingredients for incorporation into value‐added food products. The derived powders were dispersed in water and dairy cream, to investigate the effects of drying and fractionation on the dispersibility and solubility of phenolic compounds. The drying techniques, hot air drying and microwave drying, applied on bilberry press cake reduced the content of total phenolics and anthocyanins. The degradation was, however, consistently small and similar for both techniques. The major anthocyanins detected in the samples were stable during drying and fractionation treatments. Fractionation of the press cake powder affected the total apparent phenolic content and composition of the different fractions. The highest phenolic content (55.33 ± 0.06 mg g−1 DW) and highest anthocyanin content (28.15 ± 0.47 mg g−1 DW) were found in the fractions with the smallest particle size (<500 μm), with delphinidin‐3‐O‐galactoside being the most abundant anthocyanin. Dispersibility of all dried powder samples was higher in dairy cream than water, and the highest level of anthocyanins was measured in samples from the powder with the smallest particle size (<500 μm), dispersed in cream. The application of drying, milling and fractionation was found to be a promising approach to transform bilberry press cake into stable and deliverable ingredients that can be used for fortification of food products with high levels of phenolic compounds.
Highlights
Berry press cake is a natural and abundant by-product of the processing of berry juices
The objective of this study was to evaluate the effects of two drying techniques—hot air drying (HAD) and microwave-assisted hot air drying (MWD)—on total phenolic content (TPC) of bilberry press cake powder and of fractionation into three different particle sizes
The drying techniques applied on bilberry press cake reduced the content of total phenolics and anthocyanins
Summary
Berry press cake is a natural and abundant by-product of the processing of berry juices. Hot air drying (HAD), referred to as convective drying, is widely used in the food industry (Askari, Emam-Djomeh, & Mousavi, 2009) During this process, hot air transfers heat to the wet fruit by convection, and thereafter, the interior part of the fruit is heated by conduction. Microwave drying is an interesting alternative, as it results in direct heating of the product without the need to heat the surrounding air. This enables fast heating rates and reduced processing time, compared to conventional techniques, which could provide beneficial effects on quality and economical aspects. Microwave heating results in internal heating of the product, creating a pressure-driven flow that mobilizes the moisture to the surface of the product, thereby minimizing structural changes in the product (Chou & Chua, 2001; Datta, 2001)
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