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Vacuum freeze-drying of biological materials is one of the best methods of water removal, with final products of highest quality. The solid state of water during freeze-drying protects the primary structure and the shape of the products with minimal volume reduction. In addition, the lower temperatures in the process allow maximal nutrient and bioactive compound retention. This technique has been successfully applied to diverse biological materials, such as meats, coffee, juices, dairy products, cells, and bacteria, and is standard practice for penicillin, hormones, blood plasma, vitamin preparations, etc. Despite its many advantages, having four to ten times more energy requirements than regular hot air drying, freeze-drying has always been recognized as the most expensive process for manufacturing a dehydrated product. The application of the freeze-drying process to plant-based foods has been traditionally dedicated to the production of space shuttle goods, military or extreme-sport foodstuffs, and specialty foods such as coffee or spices. Recently, the market for ‘natural’ and ‘organic’ products is, however, strongly growing as well as the consumer’s demand for foods with minimal processing and high quality. From this perspective, the market for freeze-dried plant-based foods is not only increasing but also diversifying. Freeze-dried fruits and vegetables chunks, pieces, or slices are nowadays majorly used in a wide range of food products such as confectionaries, morning cereals, soups, bakeries, meal boxes, etc. Instant drinks are prepared out of freeze-dried tea, coffee, or even from maple syrup enriched with polyphenol concentrated extracts from trees. The possibilities are endless. In this review, the application of freeze-drying to transform plant-based foods was analyzed, based on the recent research publications on the subject and personal unpublished data. The review is structured around the following related topics: latest applications of freeze-drying to plant-based foods, specific technological problems that could be found when freeze-drying such products (i.e., presence of cuticle; high sugar or lipid concentration), pretreatments and intensification technologies employed in freeze-drying of plant-based foods, and quality issues of these freeze-dried products.

Glass transition temperature (Tg) has been identified as a critical factor to predict quality of foodstuffs during processing or storage. Differential Scanning Calorimetry (DSC) was used to determine the Tg of 4 types of berry powders as a function of water content, and equilibrium moisture content was measured over different saturated solutions using the gravimetric method. The Guggenheim-Anderson-deBoer model was used to predict water activity (a w ). Four models were tested for their ability to predict Tg as a function of the solid fraction. The combined effects of Tg and a w were incorporated into a new mathematical expression. The expression requires the determination of Tg (dry solids) of the product and data on equilibrium moisture sorption. The mean percent error of the model predictions is less than 3.6% when compared to experimental data.

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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...

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