Effect of hermetic storage on the development of hard-to-cook characteristics and nutritional properties of mungbean (Vigna radiata (L.) R. Wilczek) and cowpea (Vigna unguiculata (L.) Walp.)

Abstract

Mungbean and cowpea samples were stored in hermetic PET-bottles and common polybags at room temperature. After 0, 2, 4, and 6 months of storage, the samples were tested for gas composition, grain hardness, cooking time, proximate composition, free fatty acid (FFA) content, phytic acid content, oxalic acid content and antioxidant properties. The oxygen content of the mungbean and cowpea samples dropped to 7.5 ± 1.7% and 10.7 ± 0.8%, respectively, within 30 days of storage in the hermetic condition compared to control. Samples stored in polybags showed a significant increase in grain hardness and cooking-time compared to the initial samples. In contrast, the grain hardness and cooking time of hermetic samples remained within acceptable levels. The FFA values of the mungbean and cowpea samples in polybags increased by approximately 33% and 40%, respectively, after 6 months. The FFA values increased by 7.5% in mungbean and 11% in cowpea stored hermetically, which was 4 times lower than the polybag-stored samples. After 6 months, the phytic acid content of the grain samples stored in PET-bottles and polybags decreased by approximately 15% and 26%, respectively. Similarly, the oxalic acid contents were also reduced in mungbean and cowpea samples stored in polybags by 14–29% compared to the hermetic samples (2–10%). The results showed that the total phenolic content of grain samples stored in polybags was approximately 32% higher compared to grain samples stored in hermetic PET-bottles and 53% higher compared to the initial samples. These results indicated that significantly lower tendency for the development of hard-to-cook defects in grain samples stored in hermetic PET-bottles. DPPH and hydroxyl free radical scavenging activities showed a significant increase with storage time in both mungbean and cowpea samples regardless of storage method. These results revealed that hermetic storage helps to prevent the development of hard-to-cook characteristics of mungbean and cowpea.