Natural Product Recovery from Bilberry (Vaccinium myrtillus L.) Presscake via Microwave Hydrolysis

Bilberry presscake, a byproduct from juice production, contains abundant polysaccharides that can be recovered by thermal treatment. In this research, microwave hydrolysis and extraction were carried out using only water as the processing medium, thus ensuring all products (mainly saccharides) are suitable for food grade status applications. This research aims to propose an approach to fulfill multiple chemicals recovery, including anthocyanins, saccharides, proteins, and even inorganic salts. Statistical analysis suggested the conversion of bilberry presscake was accurately predictable (R2 of 0.986) from conditions. Of the variables temperature, holding time, and solid content, the solid content affects conversion most significantly. A 30 min microwave hydrolysis gives mono-/disaccharides with a high total yield of 24.9%, which is more than three times the yield of a 24 h Soxhlet extraction (7.1%). The yield of rhamnose is particularly high (10.8%), most likely as a result of pectin degradation on microwave irradiation. In addition to the lab scale research, pilot scale microwave extractions are carried out with high conversion (especially glucose 4.4%, xylose 4.0%, and pectin 6.3%), suggesting the feasibility of low-temperature (95 °C) microwave hydrolysis of bilberry presscake for industrial application. With this preliminary study, it is believed microwave hydrolysis offers an efficient and green approach to convert bilberry presscake into value-added products for food industry and biorefinery.