Rehydration characteristics of freeze-dried tropical fruits

Abstract

a b s t r a c tRehydration behaviours of five freeze-dried fruits, namely, pineapple, mango, guava, acerola and papaya were investigated and related to the structural changes during drying and glass transition temperature. After freeze-drying performed under vacuum conditions (13 kPa) and initial sample temperature near to À30 C, fruits were allowed to rehydrate at 25 C in distilled water for 6 h. The Exponential, Peleg and Weibull equations were applied to fit the experimental data using non-linear regression analysis. The statistical criteria used to evaluate the goodness of fit of each equation were the coefficient of determination (R 2 ), the standard error of estimate (SEE) and the mean relative percentage deviation modulus (MRD). The Weibull equation was found to be the most adequate for describing the rehydration kinetics, since it gave the higher R 2 values and lower SEE and MRD values for all fruits examined in this study. From indices that take into account the quantity of water absorbed and the losses of solutes, it was possible to fully characterize the rehydration process of the freeze-dried fruits. Their water uptake capacity was affected not only by injuries during moisture removal but also by structural collapse induced by the rehydration process itself, which was explained using the glass transition concept.

Drying kinetics, structural characteristics and vitamin C retention of dedo-de-moça pepper (Capsicum baccatum) during convective and freeze drying

“…Table 7 also shows values of porosity (ε) for the pepper dried by the convective and freeze drying processes. The average porosity found for the samples dried by lyophilization (0.91) is close to those usually found in lyophilized fruits (Marques, 2009). The high porosities found for products from lyophilization are a result of the process itself, which employs vacuum and low temperatures.…”

“…All three plots show a sharp increase of the rehydration ratio (RR) at the beginning of the process. The same behavior was also reported for the rehydration of tropical fruits like pineapple, papaya, mango and acerola (Marques et al, 2009), as well as of carrots (Amami et al, 2007), tomatoes and onions (Krokida and MarinosKouris, 2003). Mass reconstitution of products varied from 83 to 90% with respect to the mass of the sample before the drying process.…”

“…Losses during lyophilization were around 43.7% with respect to in natura samples. Marques et al (2009) reported that vitamin C losses of lyophilized guava fruits were up to 37.3 %. The low temperatures and residual moisture content levels of lyophilization inhibit the degradation of ascorbic acid.…”

PHYSICOCHEMICAL AND SENSORY EVALUATION OF YELLOW MOMBIN ( Spondias mombin L. ) ATOMIZED POWDER

“…This technique promotes the reduction of the water activity, preventing microbiological contamination and undesirable biochemical reactions in the food (MARQUES et al, 2009).…”

Liofilização de fatias de abacaxi: avaliação da cinética de secagem e da qualidade do produto

“…Marques et al (2009) reidrataram frutas liofilizadas, entre estas abacaxi, acerola, manga, mamão e goiaba. De acordo com os resultados, apesar de o abacaxi apresentar menor capacidade de reidratação -absorver menores quantidades de água -, a fruta atingiu o equilíbrio de reidratação, caracterizado pela não alteração de sua massa, em um tempo menor quando comparada às demais frutas, com exceção da manga.…”