Physico-functional and antioxidant properties of purple-flesh sweet potato flours as affected by extrusion and drum-drying treatments

Energy efficient drying technologies for sweet potatoes: Operating and drying mechanism, quality-related attributes

Sweet potatoes (SPs) are a versatile tuberous crop used as subsistence and cash crop in raw and processed forms. The major issue with SPs is post-harvest losses, which result in noticeable quality decline because of inappropriate handling, storage, delayed transit, and sales, as well as microbiological and enzymatic activity. Drying is an excellent strategy for managing short postharvest storage life, preserving nutrients, and maximizing long-term benefits. However, several parameters must be considered before drying SPs, such as relative humidity, temperature, drying duration, size, and shape. The current review looks at the factors influencing SPs' moisture loss, drying kinetics, diverse drying methods, pretreatments, operating conditions, and their efficacy in improving the drying process, functional, and nutritional qualities. An optimal drying process is required to preserve SPs to obtain concentrated nutrients and improve energy efficiency to be ecofriendly. Drying sweet potatoes using traditional methods such as sun or open-air drying was found to be a slow process that could result in a lower quality. Various advanced drying techniques, like vacuum, infrared, freeze drying, and pretreatments such as ultrasound and osmotic dehydration, have been developed and are successfully used globally. The best-fit thin-layer models (Hii, Page, two-term, logarithmic) utilized for drying SPs and appropriate modeling methods for optimizing drying procedures are also discussed.

Feasibility of Extruded Brewer’s Spent Grain as a Food Ingredient for a Healthy, Safe, and Sustainable Human Diet

This study aimed to determine the effect of the extrusion process on the nutritional and bioactive profiles of brewer’s spent grain (BSG), contributing to nutrition security by applying a circular economy concept. Response surface methodology was used to optimize the effect extrusion parameters (moisture content, screw speed, and barrel temperature ) had on BSG’s soluble dietary fiber, free glucose, and overall antioxidant capacity. Proximate composition analyses, amino acid profile, extractable polyphenolic content, and antioxidant capacity of BSG and brewer’s spent grain extruded under optimal conditions (BSGE) were carried out. Food safety was analyzed by their microbiological quality, gluten, and acrylamide content. Optimal extrusion conditions were 15.8% of moisture content, 164.3 revolutions per min and 122.5 °C. BSGE presented 61% more soluble dietary fiber than BSG, lower digestible starch, 0.546% of free glucose, and protein quality parameters mostly like those reported for egg, soy, and milk. Despite this, BSG’s overall antioxidant capacity was not improved after thermomechanical processing; BSGE had significantly higher extractable polyphenolic content in its alkali extracts, which were determined qualitatively by high-performance liquid chromatography quadrupole time-of-flight assay in its hydro-alcoholic acid extracts. Furthermore, although it is not gluten free, BSGE is a safe food ingredient with acceptable microbiological quality and no acrylamide.

Anchovy powder enrichment in brown rice-based instant cereal: a process optimization study using Response Surface Methodology (RSM)

There is a need for expanding the utilization of small fish as they constitute an undervalued and important source of protein and micronutrients in many developing countries suffering from micronutrient deficiencies. One way to increase consumption and health benefits is to add nutrient-rich fish meal into staple food ingredients. In this study, Response Surface Methodology (RSM) was applied to optimize the processing of an instant rice-based cereal enriched with anchovy powder. The Box-Behnken design was used to study the effect of principal processing variables (drying temperature, drum rotation speed, and slurry solids concentration) on product water activity, color, bulk density, and water solubility index. Viscosity, consistency, and cohesiveness of the reconstitute cereal were also evaluated. Empirical models were developed to describe the relationship between independent and dependent variables and showed regression coefficients (R 2) ranging between 71% and 98%. Higher drying temperatures resulted in reduced water activity, darker product color, and lower consistency. While drum speed influenced (p < .05) product color and water-binding capacity, bulk density, and consistency of the reconstituted product was associated with slurry solids concentration. Optimal processing conditions obtained from the study were temperature of 130°C, drum speed of 9.3 rpm, and solids concentration of 20.5%. These conditions would be useful in the production of brown rice-based instant cereal enriched with anchovy powder with desired quality properties.

Influence of Lactic Acid Bacteria Fermentation on Physicochemical Properties and Antioxidant Activity of Chickpea Yam Milk

This study aimed to evaluate the influence of lactic acid bacteria fermentation on the physicochemical properties and antioxidant activity of chickpea yam milk. Four groups of chickpea milk were prepared through fermentation with lactic acid bacteria for quality and functionality improvement. Results indicate that the polysaccharide content of four samples declines during the fermentation process, and their infrared spectrums are similar with a slight difference in the transmittances of some characteristic bands. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) profiles of four samples with 24 h fermentation showed a band disappearance in the range of 94.3 KDa and generation of many small-molecule peptides, revealing the protein degradation during fermentation. The moderate enzymatic hydrolysis had no adverse effect on the texture and color of the samples. A substantial increase in DPPH, ABTS radical scavenging rates, and FRAP value was observed after 12 h fermentation, especially the CPBY sample. The present results indicate that lactic acid bacteria fermentation can be used to improve the physicochemical properties of samples and enhance their antioxidant activity.

Response Surface Methodology for Optimization of Process Parameters and Antioxidant Properties of Mulberry (Morus alba L.) Leaves by Extrusion

Mulberry (Morus alba L.) leaves (MLs), originally used to feed silkworms, have recently been recognized as a food ingredient containing health-beneficial, bioactive compounds. In this study, the extrusion process was applied for the enhancement of the amount of extractable flavonoids from MLs. Extrusion conditions were optimized by water solubility index, total phenolic content, and total flavonoid content (TF) using response surface methodology, and antioxidative stress activities were evaluated in macrophage cells. According to the significance of regression coefficients of TF, the optimal extrusion parameters were set as barrel temperature of 114 °C, moisture feed content of 20%, and screw speed of 232 rpm. Under these conditions, the TF of extruded ML reached to 0.91% and improved by 63% compared with raw ML. Fifteen flavonoids were analyzed using ultra-high-performance liquid chromatograph coupled with photodiode array detection and quadrupole time-of-flight mass spectrometry (UPLC-PDA-QTOF/MS), and the extrusion resulted in increases in quercetin-3-gentiobioside, quercetin-3,7-di-O-glucoside, kaempferol-3,7-di-O-glucoside, rutin, isoquercitrin, and moragrol C. Besides, regarding antioxidative activity, extruded ML water extract inhibited the production of H₂O₂-induced reactive oxygen species and attenuated nuclear morphology alterations in macrophage cells. The findings of this study should be useful in food processing design to improve the extractable functional compounds in MLs.

Effects of processing on onion skin powder added extrudates

It is possible to enhance the functional properties of extruded products with the inclusion of fruit and vegetable by-products. Onion skin, a rich source of quercetin and fiber, is considered as waste in the industry and can be used as an alternative ingredient to improve the nutritional value of the extruded products. Three levels (3, 6, and 9%) of onion skin powder (OSP) were added to wheat flour and compared with control (0% OSP). The effect of the extrusion process on accessible quercetin, total phenolic content, and antioxidant activity of the samples were investigated. In addition, carbohydrate digestibility analyses were conducted for the products. Mass spectrometry (LC-MS/MS) results indicated that increasing the OSP level increased the quercetin content. The process caused the release of the entrapped quercetin from OSP, which was revealed by significantly higher quercetin levels for the extrudates. Some of the quercetin was lost during in vitro digestion process. Increasing the OSP level increased antioxidant activity and total phenolic contents of the samples. Total phenolic contents decreased significantly after the processing, yet antioxidant activities were not affected. The extruded products showed high amounts of rapidly available glucose (69.5 g/100 g). The OSP enhancement did not change the carbohydrate digestibility of products. The results indicated that the extrusion process could increase the level of accessible bioactive ingredients, and the level of functional compound addition can be optimized further.

Chemical constituents and health effects of sweet potato

Sweet potatoes are becoming a research focus in recent years due to their unique nutritional and functional properties. Bioactive carbohydrates, proteins, lipids, carotenoids, anthocyanins, conjugated phenolic acids, and minerals represent versatile nutrients in different parts (tubers, leaves, stems, and stalks) of sweet potato. The unique composition of sweet potato contributes to their various health benefits, such as antioxidative, hepatoprotective, antiinflammatory, antitumor, antidiabetic, antimicrobial, antiobesity, antiaging effects. Factors affecting the nutritional composition and bio-functions of sweet potato include the varieties, plant parts, extraction time and solvents, postharvest storage, and processing. The assays for bio-function evaluation also contribute to the variations among different studies. This review summarizes the current knowledge of the chemical composition of sweet potato, and their bio-functions studied in vitro and in vivo. Leaves, stems, and stalks of sweet potato remain much underutilized on commercial levels. Sweet potato can be further developed as a sustainable crop for diverse nutritionally enhanced and value-added food products to promote human health.

Effect of enzymatic (thermostable α-amylase) treatment on the physicochemical and antioxidant properties of extruded rice incorporated with soybean flour

In order to determine the effect of enzymatic extrusion on the physicochemical and antioxidant properties of rice/soybean mixture, different mass ratios (100/0, 95/5, 85/15, 70/30, 50/50 and 25/75%, w/w) were treated with thermostable α-amylase. The reduced special mechanical energy and the enhanced product temperature were closely and regularly linked with the increase of soybean content. The bulk density and water solubility index increased, and the water absorption index and viscosities decreased remarkably after enzymatic extrusion, however, the modification caused by α-amylase were dramatically eliminated with the increase of soybean content to ∼50%. Moreover, the addition of enzyme exhibited an improvement of the total phenolic/flavonoid content (TPC/TFC) and antioxidant capacities compared to traditional extrusion. The TPC/TFC retention of extrudate (ratios of 85/15 and 70/30%) attained over 90%, but dramatically decreased (72.91 and 67.81%, respectively) with soybean added to 75%, probably due to the great reduction of starch substrate for enzymatic hydrolysis.

The Effects of Fortification of Legumes and Extrusion on the Protein Digestibility of Wheat Based Snack

Cereal food products are an important part of the human diet with wheat being the most commonly consumed cereal in many parts of the world. Extruded snack products are increasing in consumer interest due to their texture and ease of use. However, wheat based foods are rich in starch and are associated with high glycaemic impact products. Although legume materials are generally rich in fibre and protein and may be of high nutritive value, there is a paucity of research regarding their use in extruded snack food products. The aim of this study was to prepare wheat-based extrudates using four different legume flours: lentil, chickpea, green pea, and yellow pea flour. The effects of adding legumes to wheat-based snacks at different levels (0%, 5%, 10%, and 15%) during extrusion were investigated in terms of protein digestibility. It was observed that fortification of snacks with legumes caused a slight increase in the protein content by 1%–1.5% w/w, and the extrusion technique increased the protein digestibility by 37%–62% w/v. The product developed by extrusion was found to be low in fat and moisture content.