Effect of Spontaneous Lactic Acid Fermentation on Physico-Chemical Properties of Sweet Potato Flour

A Mini Review of Physicochemical Properties of Starch and Flour by Using Hydrothermal Treatment

Starch and flour from various plants have been widely used for sundry applications, especially in the food and chemical industries. However, native starch and flour have several weaknesses, especially in functional, pasting, and physicochemical properties. The quality of native starch and flour can be improved by a modification process. The type of modification that is safe, easy, and efficient is physical modification using hydrothermal treatment techniques, including heat moisture treatment (HMT) and annealing (ANN). This review discusses the hydrothermal modifications of starch and flour, especially from various tubers and cereals. The discussion is mainly on its effect on five parameters, namely functional properties, morphology, pasting properties, crystallinity, and thermal properties. Modification of HMT and ANN, in general, can improve the functional properties, causing cracking of the granule surface, stable viscosity to heat, increasing crystallinity, and increasing gelatinization temperature. However, some modifications of starch and flour by HMT and ANN had no effect on several parameters or even had the opposite effect. The summary of the various studies reviewed can be a reference for the development of hydrothermal-modified starch and flour applications for various industries.

Mineral Content, Functional, Thermo-Pasting, and Microstructural Properties of Spontaneously Fermented Finger Millet Flours

Finger millet is a cereal grain which is superior to wheat and rice in terms of dietary fibre, minerals, and micronutrients. Fermentation is one of the oldest methods of food processing, and it has been used to ferment cereal grains such as finger millet (FM) for centuries. The aim of this study was to investigate the impact of spontaneous fermentation (SF) on mineral content, functional, thermo-pasting, and microstructural properties of light- and dark-brown FM flours. Spontaneous fermentation exhibited a significant increase in the macro-minerals and micro-minerals of FM flours. In terms of functional properties, SF decreased the packed bulk density and swelling capacity, and it increased the water/oil absorption capacity of both FM flours. Spontaneous fermentation had no effect on the cold paste viscosity of FM flours. However, significant decreases from 421.61 to 265.33 cP and 320.67 to 253.67 cP were observed in the cooked paste viscosity of light- and dark-brown FM flours, respectively. Moreover, SF induced alterations in the thermal properties of FM flours as increments in gelatinisation temperatures and gelatinisation enthalpy were observed. The results of pasting properties exhibited the low peak viscosities (1709.67 and 2695.67 cP), through viscosities (1349.67 and 2480.33 cP), and final viscosities (1616.33 and 2754.67 cP), along with high breakdown viscosities (360.00 and 215.33 cP) and setback viscosity (349.33 and 274.33 cP), of spontaneously fermented FM flours. Scanning electron microscopy showed that SF influenced changes in the microstructural properties of FM flours. The changes induced by SF in FM flours suggest that flours can be used in the food industry to produce weaning foods, jelly foods, and gluten-free products that are rich in minerals.

Hot air-assisted radio frequency drying of grated potato (Solanum tuberosum L.): Drying behavior and the associated effect on characteristics of potato flour

In this study, drying of grated potato in a hot air-assisted radio frequency system (HA-RF) and the associated effects on the final potato flour quality were studied. The drying behavior of the grated potatoes at different electrode distances (70-90 mm) and sample thickness (2-4 cm) was investigated. The safe drying (without burning tendency) of the maximum amount of sample (1000 g) in a reasonable drying time was carried out at 80 mm of electrode gap and 4 cm of sample thickness. HA-RF drying kinetics were studied and compared with hot air (HA) and radio frequency (RF) (without hot air) drying methods. HA-RF drying increased drying rate and shortened drying time by about 58% and 70% compared to HA and RF drying, respectively. The properties of the final potato flour obtained after HA-RF drying were also compared with those produced by RF, HA, and freeze drying. The flour obtained by HA-RF was superior to RF and HA dried samples with better retention of cellular microstructure and color. The drying method significantly affected the functional properties, thermal characteristics, pasting properties, and other characteristics of potato flours. PRACTICAL APPLICATION: HA-RF as an alternative drying technology was used for the first time to produce potato flour. The functional, thermal, and structural properties of the HA-RF dried product were compared with those dried by HA, RF, and freeze drying. The results of this study ensured very useful information for the use of potato flour obtained by different drying methods in the development of products with specific functional and rheological properties.

Improving Phenolic Bioactive-Linked Functional Qualities of Sweet Potatoes Using Beneficial Lactic Acid Bacteria-Based Biotransformation Strategy

Beneficial lactic acid bacteria (LAB) based fermentation is an effective biotransformation strategy to preserve and improve the human health-supporting functional qualities of plant-based food substrates. In this study, a food grade strain of Lactiplantibacillus plantarum was recruited to improve the retention, stability, and bioavailability of phenolic bioactives to enhance the antioxidant, anti-hyperglycemic, and anti-hypertensive functional qualities of three flesh-colored sweet potato varieties, Murasaki (off-white-fleshed), Evangeline (orange-fleshed), and NIC-413 (purple-fleshed). Liquid (cold water) extracts of the sweet potatoes, which are relevant for food grade applications, were fermented for 72 h at 37 °C. Total soluble phenolic content, phenolic profile, antioxidant, anti-hyperglycemic, and anti-hypertensive benefits relevant functional properties of fermented and unfermented sweet potato extracts were evaluated at 0, 24, 48, and 72 h time points using in vitro assay models. Overall, high total soluble phenolic content and total antioxidant activity were observed at 24 h, retaining this high level even after 72 h of fermentation. Additionally, moderate to high α-amylase, α-glucosidase, and angiotensin-I-converting enzyme inhibitory activities were observed in the fermented sweet potato extracts. The results suggested that LAB-based fermentation is an effective post-harvest processing strategy for a higher retention of phenolic bioactives and concurrently improves the human health protective bioactive functional qualities of sweet potatoes.

Trend of Modification by Autoclave at Low Pressure and by Natural Fermentation in Sweet Potato and Cassava Starches

Sweet potatoes (Ipomoea batatas L.) and cassava (Manihot esculenta C.) are part of the largest food crops in many countries. They have good nutritional value because, in addition to containing vitamins, minerals, carotenoids, and anthocyanins in varied contents, due to the existence of various colors of their pulps, they have starch as their major constituent. As such, they are considered valuable raw materials for the food factory. The starch granules have distinct morphologies and properties, related to the type of cultivar, planting conditions, storage, and processing, which in turn can affect the quality of the final products to which they have been added. The use of native starches in the food industry has limitations, which can be improved by modifications. Physical methods, as they are associated with green technology, and do not pollute the environment, have demonstrated great potential for this purpose. Both modifications—by autoclave at low pressure and natural fermentation—have shown potential in modifying these starches.

Nutritional and functional properties changes during facultative submerged fermentation of gadung (Dioscorea hispida Dennst) tuber flour using Lactobacillus plantarum

This work aims to examine the influence of flour concentrations (5%–25% w/v), inoculum loading (2.5%–15% v/v), and fermentation time (0–144 h) on the nutritional and functional properties of gadung (Dioscorea hispida Dennst) tuber flour. The flour was microbiologically treated through facultative submerged fermentation using Lactobacillus plantarum. The carbohydrate, lipid, protein, fiber and ash contents were reduced by fermentation, while moisture content was increased. In general, the swelling power and the solubility of fermented flour were below those of the native flour. Carboxyl group content increased with fermentation time, whereas no clear trend was found for carbonyl group. The amylose content of the fermented flour was larger than that of the native flour, which most probably was due to the depolymerization of amylopectin branches to form new amylose-like molecules. The best fermentation conditions were flour concentration of 10% (w/v), inoculum loading of 5% (v/v), and fermentation for 48 h.

Effects of Fermentation on Compositions, Color, and Functional Properties of Gelatinized Potato Flours

This study investigated effects of fermentation on compositions, color, and functional properties of gelatinized potato flours from Atlantic and Kexin No.1 cultivars. Atlantic flour (AF) and Kexin No.1 flour (KF) were fermented using 1% yeast concentration, respectively. Fermentation further improved the nutritional and physicochemical features of gelatinized potato flours by means of increased protein and ash contents, and decreased the levels of moisture, lipid, soluble amylose, amylopectin, and total starch. The lightness and whiteness of potato flours were enhanced with the increase in fermentation time. There are gradual increases in water absorption index, emulsifying capacity and emulsifying stability of potato flours during fermentation. However, bulk density of them slightly reduced with the increase in fermentation time. In addition, fermentation has no significant effect on freeze-thaw stability of gelatinized potato flours. These results indicate that yeast fermentation could enhance certain processing characteristics of potato flours and improve the applicability of them in food formulations. PRACTICAL APPLICATION: Lately, China has started national project regarding the use of potato flour in foods. However, due to dark color and low protein content of potato flours, their application in food formulations was limited. This study analyzed the possible mechanisms by which yeast fermentation improved the nutritional and functional characteristics of Atlantic flour (AF) and Kexin No. 1 flour (KF). From applications standpoint, findings of this study could provide knowledge on the selection of potato flours for various food formulations.