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| Author(s): |
Poliana Moser
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São José do Rio Preto. 2016-03-21. |
| Institution: | Universidade Estadual Paulista (Unesp). Instituto de Biociências Letras e Ciências Exatas. São José do Rio Preto |
| Defense date: | 2016-02-25 |
| Advisor: | Vânia Regina Nicoletti Telis; Isidro Hermosín Gutiérrez |
| Abstract | |
Grape juice has a high content of anthocyanins, with high antioxidant capacity and great potential to be used as a natural dye. Nevertheless, drying of fruit juices by atomization presents complications due to stickiness and high hygroscopicity of powders, which cause problems during processing and storage of the product. An alternative to facilitate drying is the addition of carriers that also play the role of encapsulants. The aim of this work was to produce grape juice powders by spray drying, using blends of maltodextrin and soy or whey protein as carrier agents, in order to protect the anthocyanins and to obtain a stable product with respect to physical and chemical changes. In a first step, the influence of process conditions on yield, moisture, solubility and color of powdered juice was evaluated. The conditions selected to perform drying of juice were: inlet-air temperature of 140 °C, air flow of 500 L/h, feed flow rate of 2 mL/min and low concentration of carrier. Subsequently, the use ofdifferent carriers - blends of soy protein isolate with maltodextrin (SM) and whey protein concentrated of milk with maltodextrin (WM) – was assessed on yield, solubility, anthocyanin retention, encapsulation efficiency (EE), color and morphology of the microspheres. The carrier agent concentration (CAC, g of carrier/g of soluble solids of the juice) used was in the range of 0.65 – 1.35 to SM, and of 0.15 – 0.85 to WM, whereas the protein ratio (R, g protein/100 g carrier agent) varied between 5.86 - 34.14. The grape juice powders presented high solubility and low water content. WM blends resulted in higher yields and higher anthocyanin retention than SM blends, whereas SM blends leaded to higher encapsulation efficiency. Treatments that presented the best overall results were: CAC = 1.25, 10 % soy protein; CAC = 1.00, 5.86 % soy protein; CAC = 0.75, 30 % whey protein; and CAC = 0.85, 20 % whey protein, which were coded as 1SM, 2SM, 1WM e 2WM, respectively. The powdered juices with the selected carrier formulations were evaluated for particle size distribution, water sorption isotherms, glass transition temperature (Tg), stickiness and light stability of anthocyanins. The sorption isotherms were classified as type II and the GAB model was well fitted to experimental data. The glass transition temperature decreased with the increase in water content, confirming the plasticizing effect of water. Regarding light stability, 1SM treatment showed the best anthocyanin protection. Finally, the stability of phenolic compounds and antioxidant activity of powdered grape juice - stored at 5, 25 and 35 ºC up to 150 days - were evaluated. The microspheres formulated with 1SM, which had the largest CAC, were more effective in the preservation of anthocyanins, whereas 1WM, which had the lowest CAC, did not provide good protection. With the exception of 1SM, the treatments increased the proportion of p-coumaroylated anthocyanins over storage time. Flavonols, hydroxycinnamic acid derivatives (HCAD) and flavan-3-ol were analyzed at initial (0 day) and final storage time (150 days). After 150 days, 1SM powder decreased flavonols. All treatments decreased HCAD, independently of the storage temperature, and lost flavan-3-ol at 35 ºC. Despite of all the aforementioned losses in the studied phenolic compounds, time and temperature did not influence on the antioxidant activity of the powder and reconstituted grape juice color, after 150 days of storage. (AU) | |