Rice freshness determination during paddy storage based on solvent retention capacity

Abstract

AbstractBackground and objectivesRice is an important staple food that is often stored for long periods (e.g., 2 years) but is subject to aging effects that reduce quality. Therefore, a sensitive freshness detection method for long‐term paddy storage is required.FindingsThis study stored five varieties of Chinese paddy at 4°C, 15°C, 20°C, or 35°C for 10 months, and then analyzed their solvent retention capacity (SRC), freshness index, contents of fatty acids, amylose, protein and soluble amino acids, and their thermal and thermomechanical properties. The results show that the SRC values in water, 5% NaHCO3, 5% lactic acid, and 50% sucrose solution decreased with increases in storage temperature and duration, with no differences among the five varieties. The four SRC values were negatively correlated with an existing freshness index (D615–D690), which could not distinguish between the effects of storage temperature and duration. With the SRC values for newly harvested paddy stored at 4°C used as a reference, the mean and accumulated SRC reductions were found to increase with storage temperature and duration. A protocol for rice freshness detection was developed based on these four SRC values.ConclusionPaddy with a mean SRC reduction of ≤25% is eligible for preservation, that with a mean of 25%–30% is slightly ineligible for preservation, and that with a mean of >30% is unfit for preservation. If the sum of the four SRC reductions is ≤100%, the paddy is eligible for preservation, a sum of 100%–120% indicates that it is slightly ineligible for preservation, and a sum >120% indicates that it is unfit for preservation.Significance and noveltyThis novel method based on SRC values provides an improved way to assess the freshness of stored rice.