Effect of Temperature and Storage Time on Some Biochemical Compounds from the Kernel of Some Walnut Cultivars Grown in Romania

Abstract

Walnut kernels are appreciated not only for their mineral content, vitamins, proteins, and valuable lipids, but also for the presence of polyphenolic compounds and biogenic amines. The temperature and storage time effects on some biochemical compounds from kernels collected from eight walnut genotypes grown at the Fruit Growing Research and Extension Station (SCDP) Valcea, Romania, were studied. In general, the phenolic and carotenoid compounds followed opposite trends during short-term storage and in some cases in medium-term storage. In both cases, there was a reduction in concentration during long-term storage, which was more pronounced for carotenoids. The most efficient method for preserving the walnut kernel’s phenolic content was freezing. Keeping the walnut kernel at room temperature assured the smallest carotenoid content decrease. Depending on the walnut cultivar, the preservation of the walnut kernel can be extended to five months by storage at −20 to −18 °C without loss of phenolic compounds, while a period shorter than five months (but certainly longer than three months) could be recommended for storage at 3–4 °C. Keeping it at room temperature can be an option for a short period (about three months). None of the preservation methods was adequate if the losses recorded for carotenoids were taken into account.

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

“…Oil rancidity leads to volatile compounds and off-flavours [7,8] which are undesirable for consumption. Poor post-harvest storage practices such as elevated humidity and temperature are two of the main factors initiating oil oxidation [2,[9][10][11]. Post-harvest storage practices that alleviate or slow down oil oxidation under ambient conditions are needed to prolong the shelf life of nuts.…”

“…Nuts can be sold with or without the shell, and also with or without the testa. Post-harvest storage and processing of nuts such as removing shell and/or testa, roasting, drying and packaging affect nut oxidation leading to altered hexanal production, PV and FFA [2,10,22,23]. For example, when kernels are exposed to high (120 • C) roasting temperatures for up to 20 min, testa remaining on a kernel can reduce oil oxidation compared with kernels that have the testa removed [24].…”