Use of liquid nitrogen as pistachio peeling agent: quality parameters of kernel and skins (testa)

Abstract

Nuts peeling involves the use of high volumes of hot water (90–95°C), which results in a quality loss of the final product with a significant environmental impact. The present study exploits the use of cold nitrogen gases in order to perform an alternative technique of Liquid Nitrogen Peeling (LNP). Peeled pistachio (kernel) and skin (testa) obtained from LNP were compared with those obtained using the Traditional Blanching Peeling (TBP) method. Commercial pistachios present a peroxide value equal to 4.59±0.40 meq O₂/kg of oil. After peeling process LNP sample showed a significantly (p < 0.05) lower peroxide value (PV), equal to 5.27±0.38 meq O₂/kg of oil, in comparison to that subjected to TBP that registered the value of 10.47±1.07 meq O₂/kg of oil. Moisture content is strictly connected to the stability of the final product. In our LNP samples, pistachio kernels recorded a moisture value significantly lower (p < 0.05) compared to TBP sample, and evidenced superior colorimetric characteristics. Moreover, the resulting pistachio skin from LNP had higher values of bioactive compounds and antioxidant activity. Total anthocyanins content was almost three times higher (26.03±1.61 mg Cyanidin-3-O-glucoside eq (Cya-GE) /g sample dry weight) than that recovered from skin obtained after TBP (8.33±0.70 mg Cya-GE/g sample dry weight). Results suggest this by-product could be a resource with healthy properties that can be used in food formulations.