Foam‐mat Freeze‐drying of Apple Juice Part 2: Stability of Dry Products During Storage

Abstract

Sorption isotherms at 5, 20 and 35C and glass transition temperature as a function of water content were evaluated for foamed (3% egg white and 1% methylcellulose) and nonfoamed freeze‐dried apple juice by using the static gravimetric method and differential scanning calorimetry, respectively. Equilibrium isotherms were fitted to the Guggenheim–Anderson–de Boer equation, whereas glass transition temperature to the Gordon–Taylor model. After freeze‐drying at 20C during 48 h, the dry products were stored at different temperatures (5 and 20C) under ambient conditions or vacuum. The nutritional, physical and structural properties were assessed before and at the end of the freeze‐drying process and after storage by determining vitamin C content, solubility, color and microstructure. Freeze‐dried nonfoamed juice retained more vitamin C and was more soluble than foamed products after freeze‐drying. However, foam‐mat juice powders presented higher stability during storage at 20C, which agreed with their higher values of glass transition temperature. Freeze‐dried juice stored at this temperature collapsed showing a decrease in solubility and a marked color change. PRACTICAL APPLICATIONS Quality of dry products depends largely on how they are stored (relative humidity, temperature, presence of light and vacuum). Degradation of flavor, color and texture occur under adverse storage conditions. Nutritional compounds such as vitamins or unsaturated fats could also be negatively affected because of oxidation reactions, which could be a function of the dehydration method or the pretreatment used to manufacture the dry product. The determination stability and quality degradation of foamed and nonfoamed apple juice products during freeze‐drying and storage of the dry products will complete the evaluation of foaming as a potential pretreatment for freeze‐drying.

Foam‐Mat Freeze‐Drying of Bifidobacterium longum RO175: Viability and Refrigerated Storage Stability

“…Moisture contents after 56 d storage of different sample materials were not different at the 5% level, however differences between average initial (day 0) and final (day 56) moisture contents were significant. RMC at 56 d of storage was slightly higher in foamed protective agents than in nonfoamed ones possibly due to increased surface area of foamed protective agents, a result which is in agreement with Raharitsifa and others () who reported that foamed freeze‐dried apple juice samples were more hygroscopic than nonfoamed ones. Despite an important increase in sample humidity during storage, glass transition temperatures just decreased up to 7.5% from the initial average value of 67.25 °C (Table ), remaining above 60 °C during storage.…”

“…This fact could be explained because of the increased surface area of foamed protective agents and consequently, the higher exposure of B. longum RO175 to oxygen and moisture during storage. Raharitsifa and others () found that foamed freeze‐dried apple juice was more stable during storage than nonfoamed one. In their case, however, composition of foamed and nonfoamed materials was different causing significant differences in glass transition temperature.…”

Development and characterization of composite edible films based on sodium alginate and pectin

“…Sorption isotherms characterize a relationship between water content and its activity at constant temperature (Sablani et al, 2007) and have been widely conduced on edible films (Shih et al, 2011). Selection of an appropriate mathematical model of sorption behaviour is a difficult task, because of complex chemical composition and structure of food (Raharitsifa and Ratti, 2010).…”

Adsorption Isotherms of Maria Biscuits from Different Brands

“…The sorption behavior of various foods and the influence of temperature on the relationship between equilibrium moisture content and water activity were studied and modeled extensively in recent years (McMinn et al . ; Raharitsifa and Ratti ; Sopade et al . ; Cladera‐Olivera et al .…”