Secagem das polpas de acerola (malpighia emarginata dc) e goiaba (psidium guajava l.) em leito de jorro: efeitos da adição do leite e da proteína do leite no desempenho do processo e caracterização do produto em pó

Abstract

The drying of acerola and guava pulp was studied in this work with bovine milk (powder and reconstituted in water) and concentrated whey protein as adjuvant, aiming the production of powders. The mixtures of individual fruits with their adjuvants, were processed in spouted bed dryer with inert particles of high density polyethylene at 70 °C. The dust production kinetics was obtained and the yield and the thermal efficiency of the process were calculated for all experiments. The physicochemical properties of mixtures were evaluated and compared to pure pulps. Produced powders were evaluated regarding their moisture content, water activity, hygroscopicity, solubility, particle size, x-ray diffraction, mineral composition of surface and the images obtained by scanning electron microscopy. Considering the low impact of freeze-drying, drying powders produced in spouted bed were compared with freeze dried pure acerola and guava powders. It also evaluated the impact of thermal processing on the retention of ascorbic acid and concentration of carotenoids in the powder, total phenolic compounds, antioxidant activity and total monomeric anthocyanins.. According to the results, the powders production and the yield was higher for mixtures of guava (45.21%) than for mixtures of acerola (23.06% on average) but in relation to thermal efficiency the results, for all the experiments regardless the fruit, were compatible and with an average value of 42.2%. The moisture of the freeze-dried powders and mixtures were between 5.28 to 7.04% for acerola and, 8.3% to 6.6% to guava. The water activity of both fruits mixtures did not suffered significant variation, 0.373 on average, registering the lowest value of 0.300 and 0.218 for freeze-dried powders of pure pulp of acerola and guava, respectively. Regarding other properties, they were poorly soluble and hygroscopic, highlighting the greater solubility, hygroscopicity and average diameter of particles of the lyophilized powders. The addition of adjuvants enriched the product in relation to calcium and protein content, noting the greater retention of ascorbic acid in mixtures with addition of dried milk (72.9 and 44.1%) when compared to powders obtained by freeze-drying (58 and 34.3% for acerola and guava respectively. Spouted bed drying was an effective way to produce acerola and guava based powders, using dairy products as drying adjuvants. The production of dried fruit extracts using milk as adjuvant is an interesting option for the food industry in the preparation of dairy products such as ice cream, yoghurts and desserts. In addition, the products presents satisfactory nutritional and bioactive attributes, with the combination of milk powder composition and the ascorbic acid content of fruit. Although the addition of a lower concentration (1%) concentrated serum protein has not affected the production of acerola powders, for guava, powder was obtained favoring the fluid dynamics of spouted bed processing. Similar strategy can be applied to different fruit pulps and represents a feasible alternative for processing fruit waste.