Yerba Maté ( Ilex paraguariensis St. Hil.): Chemical and Physical Changes under Different Aging Conditions.

The variation of different physicochemical parameters related to yerba maté quality (caffeine, water extract, total polyphenol content, color parameters and antioxidant activity) was studied in yerba maté samples obtained by three different aging methods: (1) natural aging ( NA); (2) temperature-controlled aging ( TCA); and (3) humidity- and temperature-controlled aging ( HTCA). Adsorption isotherms at low temperatures (20, 30, 40 and 50C) were also determined. Water extract and color parameters ( L and a) increased significantly during aging in the three methods studied ( P < 0.05). The results also showed that during NA the polyphenol content of yerba maté diminished ( P < 0.05), while caffeine remained constant ( P > 0.05). The antioxidant activities of yerba maté obtained by NA and HTCA were significantly higher ( P < 0.05) than the antioxidant activity of yerba maté without aging and the yerba maté obtained by TCA. These variations were explained by 0, 1 and 2 kinetic order equations. Kinetic rate constants were higher in the HTCA than in the TCA, and these values were higher than in the NA according to temperature decrease. Experimental data of equilibrium moisture content at different temperatures showed good fitting ( P < 0.05) with the three models tested ( GAB, Halsey and Henderson). No significant differences were found either with temperature or with the materials obtained using different aging methods. Although the results obtained demonstrate that different aging methods originate similar products, HTCA method is better because it provides a yerba maté with higher total polyphenol content. Practical Applications Aging is one stage in yerba maté ( I lex paraguariensis) processing. There are three methods commonly used to age yerba maté in industry, in which different air conditions (temperature and humidity) are employed. Sensorial analysis, usually carried out by expert tasters, is commonly used to control the aging method and the degree of aging of yerba maté. These tests are subjective and suffer from inconsistency and inaccuracy, so it is necessary to develop objective methods to identify the yerba maté quality, chemically or physically. This work evaluates the variation of different physicochemical parameters during the aging stage of yerba maté in order to differentiate the products obtained using the three aging methods. Data were fitted to different kinetic equations in order to predict the degree of aging and the time necessary to reach the end point. [ABSTRACT FROM AUTHOR]