Influences of pretreatment and drying methods on composition,micro/molecular structures and some health‐related functional characteristics of dietary fibre powder from orange pulp residues

Influences of pretreatment methods (washing, blanching, soaking in ethanol), drying methods (hot air‐drying, infrared‐drying, microwave‐drying) and drying temperature on selected characteristics of dietary fibre powder from orange pulp residues were investigated. Pretreatments improved the hydration properties, oil‐holding capacity and glucose dialysis retardation index, but led to losses of fibres, decreased α‐amylase inhibitory activity and aflatoxin B₁ adsorption capacity. Hydration properties, oil‐holding capacity and glucose uptake depended on the structure and porosity of the fibre, while the ability to inhibit α‐amylase and AFB₁ adsorption depended more on the content and molecular fingerprinting of the fibre. Drying condition did not significantly affect functional properties of the fibre, except for the ability to uptake glucose, inhibit α‐amylase and adsorb AFB₁ (P ≤ 0.05). Hot air‐drying at 60 °C resulted in fibre with the highest ability to decrease the rate of glucose and AFB₁ adsorption.     

Effects of Drying Temperature and Particle Size on Hydration Properties of Dietary Fiber Powder from Lime and Cabbage By-Products

The use of by-products from fruit and vegetable processing plants as sources of dietary fiber and bioactive agents is currently of interest, both from the waste management and from the production of value-added products points of view. This work aimed at studying the use of lime residues and outer leaves of white cabbage to produce dietary fiber powder, which included the study of the product pretreatment and preparation, drying, and grinding dried residues into powder. Dietary fiber content during each processing step was determined to calculate the loss of functionality of the products through the process. Hydration properties, i.e., water holding capacity (WHC) and swelling capacity (SWC), of the two residues were also determined after hot air drying at 60–80°C. The effect of particle size of dietary fiber powder, which was obtained by grinding dried residues, in the range of 63–450 μm, on the hydration properties was also evaluated and discussed.     

Invited review: Modelling quality changes of fruits and vegetables during drying: a review

Fruits and vegetables have received much attention as these materials have been reported to contain various phytochemicals, which are claimed to exert many health benefits. When extraction of bioactive compounds cannot be performed on fresh fruits and vegetables, drying needs to be conducted to keep the materials for later use. Dried fruits and vegetables have also been regarded as alternative fat‐free snacks and received more attention from the food industry during the past decade. This implies that not only nutritional changes, but also other changes including physical and microstructural changes are of importance and need to be optimised, preferably through the use of various modelling approaches. The objective of this article is to provide a brief review of some advances in modelling quality changes of fruits and vegetables during drying. These include modelling of nutritional, colour and selected physical changes. Approaches to monitoring and modelling microstructural changes are also mentioned.     

Composition Profiles and Functional Properties of Dietary Fiber Powder from Lime Residues: Effects of Pretreatment and Drying Methods

Lime residues after juice extraction have proven to be a potential raw material for producing dietary fiber (DF) powder due to their good functional properties. Compositions and antioxidant activity of DF powder from lime residues as affected by selected pretreatment (hot-water blanching and ethanolic soaking) and drying methods, viz. hot air drying, vacuum drying, and low-pressure superheated steam drying (LPSSD) at 60–80°C, were investigated. Fresh lime residues contained significant amounts of vitamin C, phenolic compounds, and flavonoids. Hesperidin was a major flavonoid and only one polymethoxyflavone (i.e., tangeretin) was detected in small amounts. A decrease in the amount of interested bioactive compounds and their antioxidant activity was noted at almost all steps of processing. Higher retention of bioactive compounds was noted when the residues were subject either to vacuum drying or LPSSD; the total antioxidant activities were 61–62% and 81–82% when being assessed by the β-carotene bleaching and DPPH assays, respectively. Vacuum drying at 80°C was the most suitable condition for preparing DF powder from lime residues due to its short required drying time and its ability to retain bioactive compounds. The in vitro analyses imply that DF powder prepared by vacuum drying at 80°C has the potential to reduce blood glucose and cholesterol levels by exhibiting high glucose retardation index (GRI) and bile acid retardation index (BRI).     

Application of Drying Technology to Control Aflatoxins in Foods and Feeds: A Review

Aflatoxins are secondary metabolites produced by certain species of Aspergillus, i.e., A. flavus, A. parasiticus, and the rare A. nomius, during their growth under favorable conditions of temperature and humidity. Aflatoxins are highly toxic compounds, which can cause acute and chronic toxicity in humans and animals. The incidence of aflatoxins in foods and feeds is relatively high in tropical and subtropical regions, where the warm and humid weather provides optimal condition for the growth of molds. As aflatoxins are very heat stable and cannot be easily eliminated by domestic cooking, rapid drying of agricultural products to reduce their moisture content is important, as this can avoid the favorable conditions for the growth of fungi. This article reviews general information on aflatoxins, products prone to be contaminated with aflatoxins, and the use of different drying techniques to control mold growth and aflatoxins production, as well as to reduce the contamination level of aflatoxins in food products.     

Effects of Food Topographical Features on Attachment and Heat Resistance of Salmonella During Drying

Changes in the topographical features of food during thermal processing, e.g., surface and bulk shrinkage during drying, may protect microbial cells from direct exposure to heat. Knowledge of the effects of the surface topographical features and their changes on microbial cell behavior is thus of interest. The objective of the present study was to investigate the effects of artificially prepared topographical features on the attachment ability and heat resistance of Salmonella on model food surface during hot air drying. Carrot was used as a model food material. Carrot sticks (3 × 1 × 1 cm) were artificially textured on one side with either shark tooth or wavy (crinkle) cut; the cut was artificially made to amplify the possible effect of surface roughness, which resembles topographical features of food surface and their changes, on the bacterial cell behavior. The degree of roughness was varied in the range of 20–80% of the total height of a stick. Approximately 0.2–0.7 log increase in the number of Salmonella was observed on the rough surfaces as compared to smooth control samples since larger surface areas were available for bacterial cell attachment. Salmonella attached on the surfaces with higher wave height also exhibited higher heat resistance (up to 2 h extra drying time was required to achieve 4-log reductions of Salmonella as compared to the time required by the control sample). However, the effect of cut pattern on bacterial cell behavior was not observed.     

Isomerisation kinetics and antioxidant activities of β-carotene in carrots undergoing different drying techniques and conditions

Carrots are known as a natural source of β-carotene. In order to preserve the latter, carrots must generally be processed, and drying is one of the most common methods for processing carrots. During drying β-carotene in carrots suffers degradation. β-Carotene degradation is generally due to thermal degradation and isomerisation. In this work, the drying kinetics as well as the isomerisation kinetics and antioxidant activities of β-carotene in carrots undergoing hot air drying, vacuum drying and low-pressure superheated steam drying (LPSSD) were determined within the temperature range of 60–80 °C and, in the case of vacuum drying and LPSSD, at a pressure of 7 kPa. A high performance liquid chromatography (HPLC) method was used to determine the β-carotene contents and its isomerisation kinetics, while the antioxidant activities of various combinations of all-trans- and cis-forms of β-carotene in carrots were evaluated using the Trolox equivalent antioxidant capacity (TEAC) assay.