Influence of the puffing degree on the shel-life of hot-air-puffed amaranth seeds

Puffed amaranth seed is commonly used in South American Countries as a breakfast cereal, as an ingredient in nutritional beverages and in a traditional snack called alegria. The aim of the present study was to evaluate the effect of the expansion degree of the seeds on the enzymatic and non-enzymatic oxidation of the amaranth oil, after two months storage at 25°C. Amaranth seeds were puffed (9 different experiments) with hot air at a temperature ranging between 270°C and 312°C. After puffing, the products of each trial were classified in three groups for dimensions (class A: mean diameter of 1.95 mm; class B: 1.56 mm; class C: 1.17 mm.) and evaluated for moisture, water activity, bulk density, starch damage, peroxide number and lipase activity. The puffing process, as evidenced by the Scanning Electron Microscope (SEM) analysis, radically changed the original grain organization leading to a very porous and highly disorganized structure. Seeds of class A presented a lower moisture content, a higher degree of starch damage, as evidenced by the viscoamylographic and by the enzymatic analyses, and a high peroxides content. On the contrary, the level of lipase inactivation was similar in the different samples. When observed by SEM, the surface of the less expanded products (class C) appeared partially protected against oxygen uptake by the presence of teguments still stuck to the endosperm. Statistical evaluation of the data evidenced that lipid oxidation was solely related to the degree of expansion independently of the puffing temperature. Therefore the possibility of increasing the shelf-life of puffed amaranth should mainly depend on oxygen removal from the package atmosphere.