ABSTRA ABSTRA ABSTRA ABSTRA ABSTRACT CT CT CT CT: I : I : I : I : Intr ntr ntr ntr ntrinsic stability and r insic stability and r insic stability and r insic stability and r insic stability and rheological pr heological pr heological pr heological pr heological proper oper oper oper operties of apple juice foams for foam mat dr ties of apple juice foams for foam mat dr ties of apple juice foams for foam mat dr ties of apple juice foams for foam mat dr ties of apple juice foams for foam mat drying w ying w ying w ying w ying wer er er er ere studied. e studied. e studied. e studied. e studied. Foams were prepared from clarified apple juice by adding various concentrations of 2 foaming agents of different Foams were prepared from clarified apple juice by adding various concentrations of 2 foaming agents of different Foams were prepared from clarified apple juice by adding various concentrations of 2 foaming agents of different Foams were prepared from clarified apple juice by adding various concentrations of 2 foaming agents of different Foams were prepared from clarified apple juice by adding various concentrations of 2 foaming agents of different nature: a protein (egg white at 0.5%, 1%, 2%, and 3% w/w) and a polysaccharide (methylcellulose at 0.1%, 0.2%, nature: a protein (egg white at 0.5%, 1%, 2%, and 3% w/w) and a polysaccharide (methylcellulose at 0.1%, 0.2%, nature: a protein (egg white at 0.5%, 1%, 2%, and 3% w/w) and a polysaccharide (methylcellulose at 0.1%, 0.2%, nature: a protein (egg white at 0.5%, 1%, 2%, and 3% w/w) and a polysaccharide (methylcellulose at 0.1%, 0.2%, nature: a protein (egg white at 0.5%, 1%, 2%, and 3% w/w) and a polysaccharide (methylcellulose at 0.1%, 0.2%, 0.5%, 1%, and 2% w/w), and whipping at different times (3, 5, and 7 min). In general, egg white foams were less 0.5%, 1%, and 2% w/w), and whipping at different times (3, 5, and 7 min). In general, egg white foams were less 0.5%, 1%, and 2% w/w), and whipping at different times (3, 5, and 7 min). In general, egg white foams were less 0.5%, 1%, and 2% w/w), and whipping at different times (3, 5, and 7 min). In general, egg white foams were less 0.5%, 1%, and 2% w/w), and whipping at different times (3, 5, and 7 min). In general, egg white foams were less stable but sho stable but sho stable but sho stable but sho stable but show w w w wed a higher degr ed a higher degr ed a higher degr ed a higher degr ed a higher degree of solidity (str ee of solidity (str ee of solidity (str ee of solidity (str ee of solidity (stronger str onger str onger str onger str onger structur uctur uctur uctur uctures), higher foaming capacity es), higher foaming capacity es), higher foaming capacity es), higher foaming capacity es), higher foaming capacity, and smaller bubble , and smaller bubble , and smaller bubble , and smaller bubble , and smaller bubble average diameter than methylcellulose foams. Foam stability increased with increasing concentrations of either average diameter than methylcellulose foams. Foam stability increased with increasin...

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.

Freeze‐drying of foamed and nonfoamed apple juice was studied in order to assess if there is a reduction in process time due to foaming. Foams were prepared by whipping apple juice with methylcellulose or egg albumin at different concentrations. Foamed and nonfoamed juice samples having different thickness and different initial weight were frozen at −40C and then freeze‐dried at 20C during 48 h under vacuum. Sample weight loss and temperature were followed at different process times. A mathematical model based on artificial neural networks was developed to represent foam kinetics and temperature curves during freeze‐drying. Foaming reduced process time if the comparison was done at equal sample thickness. However, lower density of foamed materials decreases weight load to the dryer. Unfortunately, the optimization of the process did not permit the determination of a practical minimal foam sample thickness to enhance both drying rate and dryer throughput. PRACTICAL APPLICATIONS Fruit juice powders have a large application in the food and nutraceutical industries. These powders are used as instant beverages, ingredients for bakery or extruded products and to incorporate in pharmaceutical tablets. Freeze‐drying is an excellent process to obtain a high‐quality fruit juice powder because it offers extraordinary nutritional, structure and sensorial qualities when compared with products of alternative drying process: air, vacuum, microwave and osmotic drying. However, the process cost is expensive due to the long drying times under vacuum. Process acceleration through optimization is therefore necessary in order to obtain high quality in the final products but at lower costs. This study aims to decrease the cost of the freeze‐drying process by using foaming prior to processing to increase the drying rate.