Presence of Testa and Shell Maintains Oil Stability in Almond and Canarium Nuts

Abstract

(1) Background: The oil stability of tree nuts during storage can be influenced by storage conditions such as temperature, humidity, and moisture concentration. However, few studies have assessed how the presence of testa and shell affects the oil stability of tree nuts during storage. We aimed to determine how storage conditions affect oil stability in almond and canarium, in particular, the presence of testa and storage time of nut-in-shell (NIS). (2) Methods: We measured peroxide value (PV), free fatty acid (FFA) and hexanal concentrations of almond and canarium (blanched vs. kernel-in-testa) stored at 45 °C for 24 days. We also measured PV, FFA and fatty acid composition of canarium samples at days 0 and 140 stored as NIS under ambient conditions. (3) Results: The presence of testa in almond and canarium decreased hexanal and PV concentrations at day 24 of incubation. Canarium PV and FFA concentrations increased over 140 days of storage in the shell compared to day 0. However, both PV and FFA concentrations remained within the acceptable threshold during storage. No changes in fatty acid composition were found during NIS storage. (4) Conclusions: Testa and shell could act as a natural coating, slowing down oxidation rates. Hence, long-term storage on nuts in testa or nuts in shell are recommended for tree nuts.

Understanding chemical pathways of brown centre formation in laboratory induced and conventionally dried nut-in-shell macadamia kernels

“…World tree nut production has increased by around 50 % in the past decade, due to increased demand for healthy foods, reaching values of 5.3 million tonnes in the 2020/2021 season and an annual global trade value of $USD 38 billion [ 4 ]. However, tree nuts are susceptible to multiple quality issues including lipid oxidation, free fatty acid formation, kernel immaturity, internal discolouration, insect attack and fungal contamination [ [5] , [6] , [7] ]. The term attributed with the internal discoloration of nuts differs depending on the type of nut, for example in almonds it is referred to as ‘concealed damage’, as ‘opalescence’ in pecans, and as ‘internal browning’ or ‘brown centres’ in both hazelnuts and macadamia nuts [ [8] , [9] , [10] , [11] ].…”