Study the Effects of Storage Temperature, Relative Humidity, and Packaging Material on the Shelf Life of the Milled Black Rice Packed in the Flexible Packaging Systems

Abstract

Estimated annual post-harvest losses for rice are about 10% of the global production due to unscientific processing (e.g., inadequate drying) and storage (e.g., exposure to pests and mold). Apart from undesirable physicochemical changes, rice grains are particularly susceptible to insects and molds attack during long-term storage due to the change in the moisture content in the storage/packaging system. This is even worst for traditionally cultivated and harvested indigenous rice varieties (e.g., black rice, soft rice, sticky rice, etc.). The deterioration can be controlled by monitoring and regulating the temperature and relative humidity of the air inside the storage systems. Hence, the present investigation aimed to study the effects of storage temperature, relative humidity, and packaging material on the shelf life of the milled black rice packed in two different flexible packaging systems. The two types of commercial packaging material, i.e., multilayered film (MLF consists of EVOH, HDPE, and PP woven layers) and PP woven. Twenty-five kg of milled black rice was filled in each bag, appropriately closed, and kept in room condition. The temperature and relative humidity sensors with data logger were placed in the geometrical center of the rice bags, and both the parameters were recorded at every 10 min intervals for 30 days. The results showed no significant temperature difference between the in-pack environment and the outside environment for both the materials. However, the relative humidity (RH) inside both the bags was lower than the RH of the outside environment. In case of MLF bags, relative humidity (50.8%) was lower compared to PP woven bags (60.7%) when the room environment had peak relative humidity (85.5%) during the storage periods. These results indicate that MLF bags have more resistance to water vapor permeation than PP woven bags. The relative humidity of the PP woven bags was almost similar to the environmental condition. Based on the moisture diffusion model, the predicted shelf-life values of the black rice in the MLF bags and PP woven bags are 230 days and 159 days at 38 °C and 90% RH (extreme condition), respectively. A mathematical model was developed to relate environmental and in-pack relative humidity. This investigation provided knowledge about temperature and relative humidity variation in two different packaging systems and suggested the shelf life of the milled rice.