Effects of degree of milling on nutritional quality, functional characteristics and volatile compounds of brown rice tea

This study investigated the effects of rice preparation using different degrees of milling (DOM) from 0% to 13% on the nutritional composition, functional properties, major volatile compounds and safety of brown rice tea (BRT). We found that 2% DOM reduced 52.33% of acrylamide and 31.88% of fluorescent AGEs. When DOM was increased from 0% to 13%, the total phenolic content (TPC) of brown rice tea decreased by 48.12%, and the total flavonoid content (TFC) and condensed tannin content (CTC) also decreased significantly, with the smallest decrease at 2% DOM. In addition, the inhibitory activities of α-amylase, α-glucosidase and pancreatic lipase as well as the antioxidant activity also decreased gradually. Analysis by electronic nose and gas chromatography-mass spectrometry (GC-MS) showed that alkanes, furans, aldehydes, pyrazines and alcohols were the major volatiles in BRT, with 2% DOM having the greatest retention of aroma compounds. An orthogonal partial least squares discriminant analysis (OPLS-DA) and VIP score (VIP > 1 and p < 0.05) analysis were used to screen 25 flavor substances that contributed to the differences in BRT aroma of different DOMs. These results suggest that 2% milled BRT can improve safety and palatability while maximizing the retention of flavor compounds and nutrients. The findings of this study contribute to an enhanced understanding of the dynamics of changes and preservation of aroma compounds and nutrients present during the processing of BRT.

Evaluation of Rice Degree of Milling Based on Bayesian Optimization and Multi-Scale Residual Model

Traditional machine learning-based methods for the detection of rice degree of milling (DOM) that are not comprehensive in feature extraction and have low recognition rates fail to meet the demand for fast, non-destructive, and accurate detection. This paper presents a digital image processing technology combined with deep learning to implement the classification of DOM of rice. An improved multi-scale information fusion model of the InceptionResNet-Bayesian optimization algorithm (IRBOA) was constructed based on the Inception-v3 structure and residual network (ResNet) model. It enables to automatically extract more comprehensive features of rice and determine the DOM of rice. Additionally, the important hyperparameters in the model were tuned by the BOA to optimize the recognition rate of rice DOM. The results show the hyperparameters optimized using the BOA are those that would not be chosen in manual tuning. The classification precision of the IRBOA model reached 99.22%, 94.92%, and 96.55% for well-milled, reasonably well-milled, and substandard rice, respectively, with an average accuracy of no less than 96.90%. This model improved 7.41% over the traditional machine learning model and at least 1.35% over the fashionable CNN model with strong generalization performance. This method effectively completes rapid, non-destructive, and accurate intelligent detection of rice DOM, which can supply a reliable and accurate technical mean for rice processing enterprises to guide the rice processing process.

Effect of parboiling conditions on zinc and iron retention in biofortified and non-biofortified milled rice

BACKGROUND

Zinc-biofortified rice could contribute to zinc intake in deficient populations, but processing it into parboiled rice could affect this potential benefit. Zinc and iron true retention (TR) in milled rice produced under conditions resembling household and commercial parboiled methods was evaluated. Zinc and iron TR in milled rice obtained from biofortified and non-biofortified rice subjected to different soaking temperatures during parboiling was also evaluated.

RESULTS

Conditions resembling commercial parboiling methods resulted in 52.2-59.7% zinc TR and 55.4-79.1% iron TR, whereas those used for household parboiling resulted in 70.7-79.6% zinc TR and 78.2-119.8% iron TR. Zinc TR in milled (8-16% bran removal) biofortified and non-biofortified parboiled rice was 50.6-66.8% when soaking rough rice at 20 °C and 29.9-56.0% when soaking rough rice at 65 °C; both had lower zinc TR than non-parboiled rice (58.0-80.6%). Iron TR was generally similar between milled non-parboiled and parboiled rice (26.2-67.6%) and between parboiled biofortified and non-biofortified milled rice.

CONCLUSION

Parboiling conditions used to obtain milled rice targeted for own household consumption resulted in higher zinc and iron TR compared to parboiling conditions used for milled rice targeted for markets. More zinc from the inner endosperm moved towards the outer layers at high soaking temperature, resulting in lower zinc TR for milled parboiled rice soaked in hotter water. Parboiled rice soaked at temperatures used in households could provide more zinc to diets compared to rice soaked in hotter water commonly used in large rice mills, especially when rice is extensively milled. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Effect of degree of milling on the cadmium in vitro bioaccessibility in cooked rice

Cadmium (Cd) contamination in rice grain is common worldwide. This study investigated the effect of degree of milling (DM) on the reduction of Cd in cooked rice grain and porridge (rice-to-water ratios 1:1.6 and 1:10, respectively) and Cd in vitro bioaccessibility. Cd-contaminated rice grains with DMs of 20%, 15%, and 0% were cooked and then subjected to successive digestion in a gastrointestinal environment model. Simulated-digestion juices, including saliva, gastric juice, duodenal juice, and bile juice, were used. The degree of gelatinization of cooked rice was measured and the morphological characteristics of the grain were also examined. The results showed that the Cd in vitro bioaccessibility, although less than 50% in all samples, was gradually increased with an increase of DM. The detected Cd bioaccessibility was higher at half meals (reduced grain content) when compared with full meals (full grain content). As DM increased, the surface of cooked rice grain and porridge became smoother, and the amount of fiber, fat droplets, and starch granules were gradually decreased, whereas degree of gelatinization increased. The results indicate that DM affects the Cd in vitro bioaccessibility in cooked rice by altering the gelatinization of starch. PRACTICAL APPLICATION: Degree of milling (DM) significantly influenced the in vitro bioaccessibility of cadmium (Cd) in cooked rice. This work may offer a potential solution to the rice grain with high Cd content because a limited DM will allow a low bioaccessibility of Cd.

The Effect of Degree of Milling on the Nutraceutical Content in Ecofriendly and Conventional Rice (Oryza sativa L.)

We investigated the effects of the type of rice and degree of milling (DOM) on the nutraceutical content and antioxidant activity of rice (Oryza sativa L.). The fatty acid (FA), vitamin E homolog, and phenolic contents in organic (OR), pesticide-free (PFR), and conventional rice (CR) decreased significantly with an increase in the DOM of rice grains, particularly for a DOM of 7 and 9 (p < 0.05). The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity also decreased with the DOM; particularly, this activity decreased significantly, by approximately 60%, in rice grains with a DOM between 7 and 11, as compared to that of brown rice (p < 0.05). α-Tocopherol (r = 0.854) and p-coumaric acid (r = 0.501) showed the strongest correlation with DPPH activity in each chemical group. Stepwise discriminant analysis enabled the correct original and cross-validated classification of 87.0% and 81.5% of rice types, respectively. Additionally, the original and cross-validated classification of rice DOM levels showed that, overall, 93.8% and 92.6% of rice samples were correctly classified. Our findings reveal variations in the nutraceutical levels and antioxidant activities in rice grains based on the rice type and DOM, which can help improve the nutritional evaluation of human-health-promoting rice grains.

Metabolomics Reveal Optimal Grain Preprocessing (Milling) toward Rice Koji Fermentation

A time-correlated mass spectrometry (MS)-based metabolic profiling was performed for rice koji made using the substrates with varying degrees of milling (DOM). Overall, 67 primary and secondary metabolites were observed as significantly discriminant among different samples. Notably, a higher abundance of carbohydrate (sugars, sugar alcohols, organic acids, and phenolic acids) and lipid (fatty acids and lysophospholipids) derived metabolites with enhanced hydrolytic enzyme activities were observed for koji made with DOM of 5-7 substrates at 36 h. The antioxidant secondary metabolites (flavonoids and phenolic acid) were relatively higher in koji with DOM of 0 substrates, followed by DOM of 5 > DOM of 7 > DOM of 9 and 11 at 96 h. Hence, we conjecture that the rice substrate preprocessing between DOM of 5 and 7 was potentially optimal toward koji fermentation, with the end product being rich in distinctive organoleptic, nutritional, and functional metabolites. The study rationalizes the substrate preprocessing steps vital for commercial koji making.

Impacts of degree of milling on the appearance and aroma characteristics of raw rice

BACKGROUND

Little has been reported about the sensory impact of degree of milling (DOM) on raw, uncooked rice. This study focuses on the effects of DOM, which was measured by surface lipid content (SLC), on appearance and aroma attributes of raw rice, as well as the appearance of cooked rice; greater DOM leads to lesser SLC levels.

RESULTS

Milled-rice samples with SLCs of 0.64, 0.59, 0.42 and 0.25%, as well as brown rice (2.27% total lipid content), were evaluated by trained panelists on three appearance- and five aroma-related attributes of raw rice, as well as four appearance-related attributes of the resultant cooked rice. All milled-rice samples, varying in SLC level from 0.64% to 0.25%, differed from brown rice with respect to raw-rice and cooked-rice appearance and aroma attributes. A significant sensory difference among the four raw-rice samples was present only in the degree of whiteness; however, such a difference was absent once the samples were cooked. When cooked, highly milled rice (0.25% SLC) was rated glossier than either lightly milled rice (0.64% SLC) or brown rice.

CONCLUSION

The present study demonstrated that sensory impacts of DOM on raw rice were present between brown rice and milled-rice samples, but not among the milled-rice samples varying in SLC level from 0.64% to 0.25%. The overall findings indicate that consumers may not detect appearance- or aroma-related differences among raw-rice samples ranging in SLC from 0.64% to 0.25%. © 2015 Society of Chemical Industry.