Desenvolvimento de polpa de butiá (Butia odorata) seca utilizando processos de secagem por micro-ondas e ultrassom

Abstract

The drying method must be chosen carefully in order to reduce the damage caused by heating to the physical-chemical characteristics and sensorial quality of the dried product. Thus, the objective of this work was to develop and evaluate the influence of Butia odorata pulp drying methods using hot air (HA) or microwave radiation (MW), as well as assisted methods with ultrasound pretreatment (US) on the physical-chemical characteristics, sensorial quality and volatile composition of the dry pulp, in addition to evaluating application in muffins. Drying by HA and MW at three different temperatures (50, 60 and 70 °C) was evaluated in terms of moisture reduction, drying rate, temperature distribution by infrared thermography, physical-chemical characteristics (water activity, rehydration capacity and color parameters), volatile composition and sensorial quality of the dried pulps. Additionally, the influence of pretreatment with US at different frequencies (25 and 45 kHz) and sonication time (10 and 20 min) were also evaluated. The MW drying increased the drying rate by reducing the drying time compared to HA. Infrared thermography showed heterogeneous heating with MW. The water activity and the rehydration capacity of the dry pulps by MW and HA did not differ. The color of the treatments at 50 and 60 °C in both techniques suffered less thermal degradation than drying at 70 °C. The comparison of the two techniques (HA and MW) showed that the best drying method was the process with use of MW at temperature of 60 °C because it presented sensorial characteristics similar to drying at 50 °C, but significantly shorter time. 56 volatile compounds were determined in the dry products through HA and MW, of which 40 presented odouriferous activity. In addition, 21 compounds showed GC-O odour activity, but were not detected in GC-FID and GC/MS. The methods using HA showed higher total volatile content. However, the concentration of ethyl hexanoate, considered the compound with the highest odouriferous contribution to the jelly palm fruit, did not present a significant difference between the treatments, with the exception of MW at 50 °C. The multivariate analysis demonstrated the treatment discrimination, with dry pulps at 50 and 60 °C obtaining higher aldehyde content, while HA at 70 °C preserved a higher number of esters. On the other hand, the treatments that produced off-flavours were HA at 50 °C and MW at 70 °C due to the high drying time and temperature, respectively. The pretreatments with US did not alter the drying time, however, they intensified the colour (a* and b*) of the samples. The volatile composition (49 compounds) indicated that US favours the preservation of short-chain esters, but the longer sonication time reduces the total area of volatile compounds. The preparation of muffins with different levels of substitution of wheat flour with dry jelly palm pulp (0, 5, 10 and 15%) has shown dry jelly palm pulp to be an appropriate ingredient to improve the nutritional value of muffins without affecting the technological properties and the sensorial acceptability, besides adding the characteristic smell and flavour of jelly palm fruit.