Ultrasound assisted bean soaking analysis by NIR spectroscopy

Dry red kidney bean is an important raw product for the canning industry requiring a soaking procedure as a vital processing step. The soaking process is a time-consuming one providing a great impact on the overall production rate. The main objective of the presented study was to monitor the conventional and ultrasound (US)-assisted soaking process of dry kidney beans based on the composition of the soaking water, including color parameters, conductivity, polyphenol content, antioxidant capacity and pH. The US-assisted soaking process resulted in a reduction of soaking time needed from about 4.5 h to about 2.5 h. The US-assisted soaking process did not result in a greater release of polyphenols and antioxidant capacity into the soaking water compared to the control until the swelling rate value (SRV) reached the technologically important value of 2. The a∗ and b∗ color parameters of the soaking water were found to be higher in the treated group than in the untreated group (a∗: US = 3.68, control = 1.39; b∗: US = 15.33, control = 9.62) indicating the ultrasound-enhanced migration of colorants into the soaking water. Based on NIR spectral analysis, the polyphenol content and antioxidant capacity of the soaking water could be well estimated (polyphenol content: R 2 P value of 0.863 and an average prediction error of 108.705 μMGA/L, antioxidant capacity: R 2 P value of 0.806 and a corresponding average prediction error of 90.090 μMAA/L). The SRV could be moderately estimated from NIR spectra. It can thus be concluded that US-assisted soaking can be a promising method to speed up the industrial process and thus save time, without significantly changing the valuable material content of the beans, while NIRS could be a applied as a reliable monitoring tool. • Ultrasound-assisted (US) treatment has the potential to reduce the soaking time of beans. • The substances released during the soaking process was examined objectively. • The soaking process was subjected to near-infrared spectroscopy analysis. • A comparable quantity was dissolved during both US and control soaking.