Acceleration of lipid oxidation in raw stored almond kernels in response to postharvest moisture exposure.

BACKGROUND: Almonds are an important crop in California, and increased yields necessitate that dried in-hull almonds are stored in the field for longer periods, increasing the potential for postharvest moisture exposure (e.g., rain, fog). Processors are increasingly drying these 'wet' almonds to a moisture content of <6% using low heat before the hulling and shelling process in order to reduce mechanical damage to the nutmeat. To date, there is no information on the impact that moisture exposure and drying prior to hulling and shelling has on lipid oxidation and storage shelf life of raw almonds. RESULTS: Raw almonds exposed to ≤8% moisture and subsequently dried (MEx) and almonds not exposed to moisture exposure (≤4% moisture; control) were stored under accelerated shelf life conditions and evaluated monthly over 12 months for free fatty acid (FFA) value, peroxide value (PV), and headspace volatiles. At 12 months of accelerated storage, MEx almonds have 1.4 times higher FFA and 3.5 times higher PV than the control, indicating significant oxidative damage. MEx almonds also demonstrated higher levels of headspace volatile compounds related to lipid oxidation (i.e., hexanal, octanal, hexanoic acid) throughout storage. CONCLUSION: Drying almonds exposed to postharvest moisture prior to storage results in a higher degree of lipid oxidation during storage and a significant reduction in shelf life. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Influence of post-harvest moisture on roasted almond shelf life and consumer acceptance.

BACKGROUND: The harvest weights of sweet almonds (Prunus dulcis) have significantly increased to meet consumer demand and now exceed processing facility capabilities. Crops are stockpiled for longer periods, increasing the probability of moisture exposure. Wet almonds can be mechanically dried prior to processing; however, it is unclear how this practice influences lipid oxidation, shelf-life, and consumer acceptance. To address this, almonds were exposed to 8% moisture and dried with low heat (ME). Almonds were roasted and stored under accelerated conditions for 12 months and markers of lipid oxidation, headspace volatiles, sensory attributes, and consumer liking were evaluated. RESULTS: At 7 months of storage, light roast ME almonds had higher levels of volatiles related to lipid oxidation than non-moisture exposed almonds (NME) and were significantly higher in oxidized, cardboard and painty / solvent flavors. Although untrained consumers did not show significant preferences between the light roast ME and NME almonds, there were quality losses related to lipid oxidation that trained panelists could detect. Dark roast ME almonds demonstrated significant lipid oxidation by 5 months of storage, indicating they will have a compromised shelf life. Findings also indicate that octanal, nonanal, 2-octenal, and hexanoic acid are good indicators of consumer acceptability. CONCLUSION: The results of this research illustrate that post-harvest moisture exposure with mechanical drying has a significant effect on the storage quality of roasted almonds and is most pronounced in dark roast products. © 2020 Society of Chemical Industry.