Hydrolytic rancidity and its association with phenolics in rice bran

Low temperature storage alleviates aging of paddy by reducing lipid degradation and peroxidation

The quality deterioration of paddy during storage is closely associated to lipid metabolism. To explore the effect of lipid metabolism on the texture of paddy, freshly harvested Nanjingxiangzhan (Indica rice) stored for 60 days at 15 °C and 25 °C for 60 days was investigated. Paddy stored at 15 °C showed higher contents of ATP, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, triacylglycerols, diacylglycerols, monogalactosyldiacylglycerol and digalactosyldiacylglycerol but lower levels of lysophosphatidylcholine, lysophosphatidylethanolamine, phosphatidic acid, ceramides and free fatty acids. Storage at 15 °C inhibited lipase, phospholipase D (PLD), lipoxygenase (LOX) activities and the corresponding gene expressions. Moreover, 15 °C storage retarded the rise of hardness, cohesiveness and chewiness, while delayed the reduction of gumminess and springiness. These findings suggested that maintenance in glycerophospholipids, glycerolipids and saccharolipids abundance, reduction in lysophospholipids, phosphatidic acid, ceramides and free fatty acids accumulation could contribute to enhanced internal resistance to aging in freshly harvested paddy at low temperature storage.

Characterizing the mono- and triacylglycerol lipase (MAGL and TAGL) genes from pearl millet (Pennisetum glaucum L.) and elucidating their dynamics with biochemical traits linked with rancidity

MAIN CONCLUSION

We cloned two variants of lipase gene-MAGL and TAGL from pearl millet. Lipase showed negative correlation with antioxidants and total phenolics. FAA can be used as marker for rancidity. Pearl millet is considered as "Nutri-cereal" due to its rich nutrient profile. Low keeping quality of the flour due to rancidity is one of the major problems in pearl millet. Lipases are a group of enzymes that produces free fatty acids that ultimately leads to rancidity. Very few lipases have been identified and characterized from pearl millet. Here, we have identified 2039 transcripts of lipases from pooled samples (leaf, stem and developing grains) of pearl millet using de novo transcriptomic approach and predicted 05 full length lipase variants. Further, we cloned 02 lipase genes-monoacylglycerol lipase (MAGL, acc. no. MZ590564) and triacylglycerol lipase (TAGL, acc. no. MZ590565) of 1.5 kb each from pearl millet cv. Pusa-1201. Conserved domain search analysis showed the presence of catalytic triad [GXSXG] near the active site which is signature domain of lipase family of proteins. MAGL showed maximum expression in PC-701 and TAGL in Pusa-1201 during mealy-ripe growth stage of endospermic tissue. Abundance of transcripts of both the lipases was observed in the harvested grains of PC-701. We observed negative correlation between the lipase activity and accumulation of antioxidants like total phenolic content (TPC), tannin, and total antioxidant potential (TAP). Free amino acid and reducing sugar were observed as potential markers for accessing the intensity/extent of rancidity in pearl millet flour. Thus, there is need to explore and characterize the lipase variants to connect the missing dots in rancidity pathway and to use it in genome editing using the CRISPR/Cas9 approach for the development of pearl millet lines free of off-odor and flour rancidity.

Lipase Inactivation Kinetics of Tef Flour with Microwave Radiation and Impact on the Rheological Properties of the Gels Made from Treated Flour

In recent years, many efforts are being made to produce tef-based food for its nutritive and health-promoting advantages. Tef grain is always whole milled because of its tiny grain size and whole flours contain bran (pericarp, aleurone, and germ) where major non-starch lipids could be deposited along with the lipid-degrading enzymes: lipase and lipoxygenase. As lipoxygenase shows little activity in low moisture, the inactivation of lipase is the common objective for most heat treatments to extend the shelf life of flours. In this study, tef flour lipase inactivation kinetics via hydrothermal treatments assisted using microwaves (MW) were studied. The effects of tef flour moisture level (12%, 15%, 20%, and 25%) and MW treatment time (1, 2, 4, 6, and 8 min) on flour lipase activity (LA) and free fatty acid (FFA) content were evaluated. The effects of MW treatment on flour pasting characteristics and the rheological properties of gels prepared from the treated flours were also explored. The inactivation process followed a first-order kinetic response and the apparent rate constant of thermal inactivation increased exponentially with the moisture content of the flour (M) according to the equation 0.048·exp (0.073·M) (R² = 0.97). The LA of the flours decreased up to 90% under the studied conditions. MW treatment also significantly reduced (up to 20%) the FFA level in the flours. The rheological study confirmed the presence of significant modifications induced by the treatment, as a lateral effect of the flour stabilization process.

Exploration on Varying Patterns of Morphological Features and Quality of Armeniacae Semen Amarum in Rancid Process Based on Colorimeter, Electronic Nose, and GC/MS Coupled With Human Panel

In recent years, the domestic and international trade volumes of Chinese medicinal materials (CMMs) keep increasing. By the end of 2019, the total amount of exported CMMs reached as high as US $1.137 billion, while imported was US $2.155 billion. A stable and controllable quality system of CMMs apparently becomes the most important issue, which needs multifaceted collaboration from harvesting CMMs at a proper season to storing CMMs at a proper temperature. However, due to imperfect storage conditions, different kinds of deteriorations are prone to occur, for instance, get moldy or rancid, which not only causes a huge waste of CMM resources but also poses a great threat to clinical medication safety and public health. The key issue is to quickly and accurately distinguish deteriorated CMM samples so as to avoid consuming low-quality or even harmful CMMs. However, some attention has been paid to study the changing quality of deteriorated CMMs and a suitable method for identifying them. In this study, as a medicine and food material which easily becomes rancid, armeniacae semen amarum (ASA) was chosen as a research objective, and experimental ASA samples of different rancidness degrees were collected. Then, various kinds of analytical methods and technologies were applied to explore the changing rules of ASA quality and figure out the key indicators for the quality evaluation of ASA in the rancid process, including the human panel, colorimeter, electronic nose, and GC/MS. This study aims to analyze the correlation between the external morphological features and the inner chemical compounds, to find out the specific components from "quantitative change" to "qualitative change" in the process of "getting rancid," and to discover the dynamic changes in the aforementioned key indicators at different stages of rancidness. The results showed since ASA samples began to get rancid with the extension of storage time, morphological features, namely, surface color and smell, changed significantly, and the degree of rancidness further deepened at the same time. Based on macroscopic identification accomplished via the human panel, ASA samples with varying degrees of rancidness were divided into four groups. The result of colorimeter analysis was in agreement with that of the human panel, as well as the determination of the amygdalin content and peroxide value. Moreover, there were obvious differences in the amygdalin content and peroxide value among ASA samples with different rancidness degrees. With a higher degree of rancidness, the content of amygdalin decreased, while the peroxide value increased significantly. The rancidness degree of ASA has a negative correlation with the amygdalin content and a positive correlation with the peroxide value. The newly discovered nonanal and 2-bromopropiophenone in rancid ASA samples may be the key components of "rancidity smell," and these two components would be the exclusive components that trigger "quantitative change" to "qualitative change" in the process of rancidness of ASA. This study sheds light on studying the internal mechanism of "rancidness" of CMMs and provides an important basis for the effective storage and safe medication of easy-to-get rancid herbs, and it also plays an important foundation for the establishment of a stable and controllable quality system for CMMs.