Storage time affects storage proteins and volatile compounds, and pasting behavior of milled rice

Albumin, globulin, glutelin and prolamin fractions were isolated from a Thai rice variety (cv. Khao Dawk Mali 105), which was stored at 25°C for 0-7 months and characterised by yield and protein contents. The solubility of protein under the influence of storage time was studied by extractable protein contents, while pasting properties of rice flour following storage of the grain for up to 7 months were investigated by rapid viscosity analysis (RVA). The total protein content of fresh harvest rice was decreased 19.81%. The highest contents of glutelin and globulin were 70% and 20%, respectively, while albumin and prolamin were found in relatively equal amount in rice grain. Glutelin was most significantly affected on pasting properties, while globulin affected on peak viscosity and also setback and breakdown properties, but on the lesser extent than glutelin. Albumin and prolamin affected mostly on setback. The results showed that each type of the storage proteins affected on viscosity of pasting properties of rice starch during storage. The results of viscograms from the samples provided a valid comparison of the effects of aging on pasting behavior and confirmed that each type of the stored-rice proteins affected on viscosity of pasting properties of rice starch during storage. Stored-rice protein contents had a significant positive correlation with 2-acetyl pyrroline content and a negative correlation with hexanal contents. Shorter storage time was considered to be used to preserve 2-acetyl pyrroline and stored-rice protein of the aromatic rice. Stored-rice proteins had some effects on viscosity properties of rice flour so they could be important for food applications.