Lipid degradation during grain storage: markers, mechanisms and shelf-life extension treatments

Abstract

Introduction:One of the challenges with whole grain ingredients, foods and meals is that they typically have a shorter shelf-life compared to equivalent products that contain refined grains, without a bran layer. This is primarily due to lipid degradation that leads to rancidity and is a major impediment to the further development of whole grain products. The consequent reduction in shelf life is due to the production of molecules with unpleasant scent and flavour caused by the lipid degradation which result from chemical or enzymatic modification of (primarily) bran-based lipids.The rate and extent of lipid degradation depends upon many factors including: the composition and structure of the seed/grain, the types of lipid present, the moisture content and any external catalysts such as the presence of some metals or simply exposure to light. Materials and methods:This work includes a comprehensive study of the different biological seed groups used in the food industry when creating different whole grain products included under the "whole grain" and "whole meal" label. The 11 samples selected were barley, red sorghum, white sorghum, teff, red quinoa, white quinoa, buckwheat, sunflower, flax, white chia and black chia. The samples (n=1188) were stored ground and intact under three different storage conditions at three different temperatures (4, 23, and 38°C) for up to 4 months to examine the reactions occurring in the samples: from the fresh seed (fatty acid composition), followed by lipid degradation, from hydroperoxides (hydroperoxide value), up to the volatile compounds production (head space analysis) at days 0, 2, 5, 10, 15, 20, 30, 60 and 110. Multivariate analysis was performed to identify the differences between samples, storage conditions and lipid composition. Based on these results: furan 2-ethyl-, furan 2-pentyl-, pentanal, heptanal, octanal, nonanal and 2-heptanone are the analytes that showed a statistical relation (p<0.05) and were strongly positively correlated with storage time were studied in detail. The goal was to find molecules that show a stable increase with time and could potentially be good quantitative markers of lipid degradation, so with future work and relating with sensory studies they could become markers of rancidity. A selection of samples were then used in an experiment to evaluate options to extend the shelf-life of ground whole grains, using natural treatments. The samples selected were: barley, quinoa white and flax, and they were treated with natural antioxidants (lemon myrtle and rosemary-tocopherol) and thermal treatments (dry heat and wet heat), compared with a chemical antioxidant (BHA) during storage for 14weeks at room temperature in closed vials. Headspace analysis was performed after 2, 4, 8 and 14weeks. Results:The results show that the seed fatty acid composition has a strong impact on lipid stability, except in the case of flax and chia black which based on the fatty acid composition should have been very unstable but were not. Endogenous antioxidant capacity can re...

Ethanolic Fermentation of Rye Mashes: Factors Influencing the Formation of Aldehydes and Process Efficiency

“…This substantial difference may be explained to a significant extent by the large differences in the concentrations of acetaldehyde and capronaldehyde determined in the mashes prepared by the pressureless method, compared to the samples prepared by the pressure-thermal method. Caprylaldehyde (octanal) is a product of the degradation of lipids present in cereal grains [ 42 ] and was probably degraded during the steaming of the rye grain.…”

Fatty Acid Profiles of Oil Obtained from Corn Kernels (Zea Mays L.) Preserved by a Triple Bagging System and Aromatic Plants (Lippia multiflora and Hyptis suaveolens)

“…N'kouam 34 , Al-abdalall and Al-Juraifani 29 and De Carvalho et al 31 also mentioned the effect of storage on fat composition during the respective storage of aiele fruit, coffee seeds and sunflower seeds. Moreover, Tamendjari et al 35 then Ortega et al 32 , in their study on bacterial and fungal infestations during storage of olive seeds and wheat grains, under conditions of relative humidity between 50 and 100%, would have indeed shown that the actual presence of these microorganisms negatively affected the PUFA content of the extracted oils. As for the slight variations in the SFA (PLA, STA and MGA), MUFA (OLA) and PUFA (LA, ALA, GLA, DDA and ARA) contents of the oils extracted from the triple bagging samples associated with biopesticides, they reflect the conservation the FA profile of the fat in the grains during storage Correlation analysis performed on the fatty acid profile of the different corn oil samples revealed strong positive relationships between the fatty acids PLA, STA, LA, ALA, ARA and PUFA.…”

Changes in nutritional quality-related traits of quinoa seeds under different storage conditions

“…As previously mentioned, oxidative stress can cause lipid peroxidation, which results in the degradation of unsaturated fatty acids producing free radicals that contribute to oxidative stress ( 69 ), which in turn can result in rancid odors and flavors in the seeds, decreasing their shelf life affecting their monetary value ( 70 ). Indeed, lipid peroxidation targets primarily PUFAs ( 64 ), which are of great importance for human health since diets rich in unsaturated fatty acids can contribute to cardiovascular disease prevention ( 71 ).…”

“…According to the high levels of fat found in the present and previous studies ( 29 , 72 , 73 ), elevated rates of peroxidation would have been expected. However, quinoa seeds have shown a resistance to ROS-induced peroxidation, probably due to a strong antioxidant capacity ( 70 ). Also, although the decrease in PUFAs relative content was significant at the seed oil level, this did not significantly affect the total fat content ( Figure 3A ), which in fact showed an increase after 6 months in F16 seeds (not significant in Duquesa seeds), probably due to the decrease in total seed weight after the loss of SMC ( Figure 1A ).…”

“…Quinoa seeds have an overall good antioxidant system ( 83 ) that makes them more stable over storage time ( 70 ) and also contributes to their nutritional quality and health benefits, reducing the risk of oxidative stress-related chronic diseases like cancer, cardiovascular disease, or diabetes ( 31 ). The antioxidant system in seeds is constituted by antioxidant compounds, such as vitamin E, polyphenols, and flavonoids, while the antioxidant enzymes cannot activate their function until germination due to the low moisture content.…”