Label-free quantitative proteomics of commercial rice beverages reveals the presence of high amounts of exogenous amylases

Rice milk is known for its wide range of beneficial effects on human health. Despite an increasing inclination towards rice drinks consumption, not much is known regarding the protein composition of commercial rice beverages. Hence, using a label-free quantitative proteomics approach we analyzed 9 different commercially available rice drinks and identified 259 rice proteins and 4 exogenous microbial α-amylases. Unexpectedly, exogenous α-amylases, when present, were the most abundant in terms of percentage mass. Interestingly, a very strong correlation between the amount of exogenous α-amylases and amylase inhibitors was observed and so was the correlation between α-amylases and the content of free sugars. We identified 20 potential rice allergens which, together with the exogenous microbial proteins, accounted for 32.3% of the total average percent mass. Taken together, our results have improved the understanding of the protein composition of commercial rice beverages.