INFLUENCE OF pH ON PROTEIN EXTRACTION FROM WHITE BEAN VIA ACID PRECIPITATION

Acid precipitation in aqueous medium is a widely used approach for the extraction of plant proteins, primarily due to its operational simplicity. This study aimed to compare the efficiency of protein extraction from white beans (Phaseolus vulgaris L.) using two pH values: (i) pH 3.0, commonly reported in the literature; and (ii) pH 3.5, previously identified as the isoelectric point of the proteins in the material. Initially, the beans were soaked in deionized water for 24 hours at 4 °C to facilitate hull removal. The cotyledons were then ground, filtered, and subjected to alkaline extraction at pH 10.0 under agitation for 12 h. After centrifugation (4,000 rpm, 10 min), the supernatant was collected and adjusted to the respective acidic pH values (3.0 or 3.5) to induce protein precipitation. The precipitate was subjected to successive washing and centrifugation steps (4,000 rpm, 10 min), then frozen and lyophilized. Extraction yield was determined based on the mass of the dried powder, while protein content was quantified using the Kjeldahl method (conversion factor 6.25). The resulting concentrates showed protein contents of 61.7% (pH 3.0) and 62.6% (pH 3.5), both qualifying as protein concentrates. However, extraction yield was higher at pH 3.5 (14.1%) compared to pH 3.0 (10.1%). Although protein content remained similar between conditions, the increased yield at a pH close to the isoelectric point highlights the advantage of this approach. It is concluded that protein extraction at pH 3.5 represents a promising alternative for obtaining white bean protein concentrates, with potential to improve industrial-scale extraction processes.