Evaluation of Different Storage Conditions on Rice Germ Shelf Life by FT-NIR Spectroscopy and ENose

Rice germ is a by-product of rice milling process, good source of proteins, bioactive phytochemical compounds and lipids rich in unsaturated fatty acids. For its own nature, rice germ could be interesting for human nutrition but, unfortunately, it undergoes rancidity development during storage. Heat treatments are usually applied to inactivate native lipase and slow down the enzymatic degradation. This study explored the possibility of extending germ shelf life by reducing water activity in combination with modified atmosphere packaging, without any heat treatment. Dried samples at different water activities (0.55, 0.45 and 0.36) were packed in air, nitrogen or under vacuum, and stored at 27°C for 322 days (7 sampling points). To the aim, a non-targeted approach was applied by means of an FT-NIR spectrometer in reflectance with a rotating sample holder and a portable e-nose, equipped with 10 non-specific MOS sensors. An exploratory Principal Component Analysis (PCA) on the whole dataset was performed, after a low-level data fusion, allowing to follow samples evolution during storage and identifying different clusters according to the storage condition. The observed groups were related to water activity while no interesting differences were highlighted between the modified atmosphere packaging systems. A 2D correlation map was developed combining the sensors data with the spectral information to understand relationships among NIR absorption bands and classes of chemical compounds inducing e-nose responses. In terms of correlation, the sensors could be divided in two groups negatively inter-correlated. The sensors typically ascribable to aromatic compounds (WC) were correlated with the NIR band around 4000 cm-1 while the sensors of broad range response (WS) were linked with the NIR band around 7550 cm-1. Considering the peculiar structure of the data set, multi-way analysis was applied to relate the information coming from the non-targeted methods with storage time. In conclusion, water activity was the most important parameter affecting rice germ shelf life although not a strong evolution was pointed out along time.