Functional properties of endosperm protein from size‐fractionated broken rice kernels generated after milling of parboiled and nonparboiled rice

Background and objectives The quantity and functionality of proteins in different sizes of broken rice (brokens) may inform the different pasting properties observed in rice flour derived from brokens. This study was conducted to determine properties of protein from size-fractionated parboiled and nonparboiled milled broken rice kernels. In addition, the research sought to determine the extent to which properties of proteins influence functionality of rice flour derived from the studied brokens. Findings Whole kernels and medium brokens of nonparboiled rice recorded the highest quantity and yield of protein isolate, while the lowest was recorded in large brokens. A strong negative correlation existed between sample protein content and the size of parboiled brokens. Parboiled samples had decreased protein extractability than nonparboiled samples. Emulsifying activity (EA) of parboiled rice had a significantly strong negative linear association with size of brokens. Emulsifying stability (ES) on the other hand had a significantly strong positive linear association with size of brokens, and about 82% of the variation in ES was explained by size. The trend was opposite in the nonparboiled stream with ES having a strong negative linear association with size. A very strong positive linear association existed between foaming capacity (FC), foaming stability (FS), and size of nonparboiled samples. Surface hydrophobicity (SH) was significantly different among parboiled and nonparboiled rice, with weak positive correlations existing between SH and size of parboiled and nonparboiled samples. Solubility curves in nonparboiled stream were more uniform than the parboiled stream. Strong significant positive correlations existed between peak, trough, breakdown, final, setback viscosities, and ES. A strong positive linear association was observed between peak, trough, final viscosities, and FS. Differences in protein contents of whole kernels and size-fractionated brokens may be attributed to either the variations in the distribution of inherent components of the kernel or variations in milling efficiency. Results in this research are specific for long-grain hybrid rice and may vary depending on cultivar and environmental factors. Conclusions Proteins influence the pasting properties of brokens. Understanding the functional properties of size-fractionated broken rice kernels from parboiled and nonparboiled streams is essential in directing the right kind of brokens to the right end-use. Significance and novelty This study provides useful information to better utilization and value addition of brokens.