The effect of roasting, irradiation and storage on the main nutrients of three varieties of almonds

Abstract

The effects of processing (irradiation and heat treatment) and storage on the main nutrients (carbohydrates, proteins and lipids) of almonds (Prunus amyqdalus Batsch) have been investigated. Two varieties of Iranian almonds: P. amygdalus var. hard shelled, and P. amygdalus var. fragile, and one American variety, P. amygdalus var. semi-hard have been used in the present study. Variations between the nutrient composition of the different varieties were observed, and the range was between 93 and 132 mg/g for carbohydrates; 170 and 180 mg/g for proteins and 400 and 500 mg/g for lipids. The almonds were then subjected to the following three processes:1. A sample of shelled almonds was subjected to 2 Mrad irradiation using 60Co. Changes followed similar trends in the three almond varieties after irradiation. There were no significant losses in total available carbohydrates, total proteins and total lipids, whereas increases were observed in free amino acids, free sugars and free fatty acids. Storage of the irradiated almonds at 22°C for one year did not bring about any changes in total available carbohydrates, total protein and total lipids. However, there were changes in the individual free sugar fractions, while no changes were observed in free amino acids and in free fatty acids.2. Samples of shelled almonds were pre-soaked in 17% salt solution for 4 hours with slow agitation. After removing them from the solution, the salted nuts were transferred to a rotary drum and dried at 70°C for one hour, until the moisture taken up during the soaking treatment was removed. The temperature was then raised to 120°C within 30 minutes and roasted for 20 further minutes. Losses occurred in both carbohydrates and proteins, while the total lipid content remained unchanged after the above processing. Decreases were noted in free amino acids and in free sugars, but there were increases in free fatty acids. Storage at 22°C for one year resulted in no further losses of carbohydrates and proteins. Free amino acids increased, indicating some protein hydrolysis. A further increase in free fatty acids was observed. 3.A sample of shelled almonds was first roasted as described under (2) and then irradiated as described under (1); this being referred to as combined processing (dual treatment). The same three nutrients followed very similar trends to those found in roasted samples. So, on the whole, irradiation at 2 Mrad seems to preserve the nutrients of almonds much better than does roasting, especially during storage for one year.