A comprehensive review of the mechanism, changes, and effect of deep fat frying on the characteristics of restructured foods

Restructured foods are a blend of various ingredients that are dried or fried to obtain a ready-to-eat product. Several frying techniques have been employed viz., deep fat, microwave, vacuum, air, and spray frying. Deep-fat frying is the most common technique used for products that have improved texture and sensory characteristics. It facilitates various transformations that include starch gelatinization, protein denaturation, nutrient loss, non-enzymatic browning, lipid oxidation, etc. This physicochemical change alters both the product and the fried oil quality. The frying conditions will also influence the product characteristics and affect the properties of the fried product. This review focuses on the mechanisms and transformations during deep fat frying. The properties, namely physical, chemical, sensory, thermal, rheological, and microstructural changes of restructured foods were discussed. Thus, a better understanding of mechanisms and properties at optimum frying conditions would yield the desired product quality.

Review of formation mechanisms and quality regulation of chewiness in staple foods: Rice, noodles, potatoes and bread

Staple foods serve as vital nutrient sources for the human body, and chewiness is an essential aspect of food texture. Age, specific preferences, and diminished eating functions have broadened the chewiness requirements for staple foods. Therefore, comprehending the formation mechanism of chewiness in staple foods and exploring approaches to modulate it becomes imperative. This article reviewed the formation mechanisms and quality control methods for chewiness in several of the most common staple foods (rice, noodles, potatoes and bread). It initially summarized the chewiness formation mechanisms under three distinct thermal processing methods: water medium, oil medium, and air medium processing. Subsequently, proposed some effective approaches for regulating chewiness based on mechanistic changes. Optimizing raw material composition, controlling processing conditions, and adopting innovative processing techniques can be utilized. Nonetheless, the precise adjustment of staple foods' chewiness remains a challenge due to their diversity and technical study limitations. Hence, further in-depth exploration of chewiness across different staple foods is warranted.

Wheat gluten structure and (non-)covalent network formation during deep-fat frying

The aim of this work was to investigate wheat gluten protein network structure throughout the deep-frying process and evaluate its contribution to frying-induced micro- and macrostructure development. Gluten polymerization, gluten-water interactions, and molecular mobility were assessed as a function of the deep-frying time (0 - 180 s) for gluten-water model systems of differing hydration levels (40 - 60 % moisture content). Results showed that gluten protein extractability decreased considerably upon deep frying (5 s) mainly due to glutenin polymerization by disulfide covalent cross-linking. Stronger gliadin and glutenin protein-protein interactions were attributed to the formation of covalent linkages and evaporation of water interacting with protein chains. Longer deep-frying (> 60 s) resulted in progressively lower protein extractabilities, mainly due to the loss in gliadin protein extractability, which was associated with gliadin co-polymerization with glutenin by thiol-disulfide exchange reactions. The mobility of gluten polymers was substantially reduced during deep-frying (based on the lower T2 relaxation time of the proton fraction representing the non-exchanging protons of gluten) and gluten proteins gradually transitioned from the rubbery to the glassy state (based on the increased area of said protons). The sample volume during deep-frying was strongly correlated to the reduced protein extractability (r = -0.792, p < 0.001) and T2 relaxation time of non-exchanging protons of gluten proteins (r = -0.866, p < 0.001) thus demonstrating that the extent of gluten structural expansion as a result of deep-frying is dictated both by the polymerization of proteins and the reduction in their molecular mobility.

Effect of pre-drying and post-frying holding treatments on the oil absorption and quality of fried batter-coated peanuts

In this study, the effect of pre-drying and post-frying holding treatments on the oil absorption and the quality of the fried batter-coated peanuts were explored. The results showed that hot air drying and microwave drying induced the gelatinization of starch in the batter before frying. The thermodynamic properties of starch in the batter after frying indicated that pre-drying could protect the orderliness of the starch. CLSM images showed that the pre-drying treatment reduced the number of large oil spots on the surface of batter of fried batter-coated peanuts. SEM observation revealed that the structure of the batter treated with pre-drying was denser and the number of large pores was reduced after frying. The post-frying holding treatment improved the color and texture of the batter-coated peanuts. In conclusion, the pre-drying and post-frying holding treatment can reduce the oil content and improve the fracturability of the fried batter-coated peanuts.

Effect of cooking methods on nutritional value and microbial safety of edible rhinoceros beetle grubs (Oryctes sp.)

Although edible rhinoceros beetle (Oryctes sp.) larvae are popularly consumed in many countries worldwide, they are prepared using different methods such as boiling, roasting, toasting, and deep-frying, whose effect on nutritional value and microbial safety is scarcely known. Here we investigated the effect of these methods on the nutritional value and microbial safety of Oryctes sp. larvae. Our hypothesis was that cooking the grubs using the four methods had no effect on their nutritional content and microbial loads and diversity. The grubs were analyzed for proximate composition, and fatty and amino acid profiles using standard chemical procedures; and microbial safety using standard culturing procedures. Deep-frying reduced protein and carbohydrate content, but elevated fat content. Boiling lowered ash content, but increased fibre and carbohydrate composition. Roasting and toasting increased protein and ash contents, respectively. Forty fatty acids were detected in the larvae, of which levels of only five were not significantly affected by cooking method, while the levels of the others were differentially affected by the different cooking methods. Amino acid profiles and levels were largely comparable across treatments, but lysine and arginine were higher in all cooked grubs than raw form. All the cooking methods eliminated Enterobacteriaceae, Shigella sp. and Campylobacter sp. from the grubs. Except boiling, all methods reduced total viable count to safe levels. Salmonella sp. were only eliminated by toasting and roasting; while boiling promoted growth of yeast and moulds. Staphylococcus aureus levels exceeded safety limits in all the cooking methods. These findings offer guidance on the type of method to use in preparing the grubs for desired nutritional and safety outcomes.

Oil Frying Processes and Alternative Flour Coatings: Physicochemical, Nutritional, and Sensory Parameters of Meat Products

The frying process changes can be desirable and undesirable, involving the physicochemical, nutritional, and sensory aspects, depending on the food and oil properties and the frying process. In this context, alternative flours emerge as a strategy for adding value to the food since they are rich in fiber, vitamins, and minerals, contributing to the variability of ingredients and the full use of food, including residues such as seeds and husks. This narrative review aims to gather current scientific data addressing the alternative flour coatings on breaded meat, mainly chicken, products to evaluate the effects on fried products' nutritional value, physicochemical parameters, and sensory attributes. Scopus, Science Direct, Springer, and Web of Science search bases were used. This review showed that alternative flours (from cereals, legumes, fruits, and vegetables) used as coatings increase water retention and reduce oil absorption during frying, increase fibers and micronutrient content, which are not present in sufficient quantities in commonly used flours due to the refining process. These flours also reduce gluten consumption by sensitive individuals in addition to favoring the development of desirable sensory characteristics to attract consumers. Therefore, frying processes in oil promote a reduction in humidity, an increase in oil absorption and energy content, and a decrease in vitamin content. In this context, coatings based on alternative flours can reduce these adverse effects of the frying process.

A review on the frying process: Methods, models and their mechanism and application in the food industry

Frying is one of the most popular and traditional processes used in the food industry and food services to manufacture products that are high in quality and with unique sensory characteristics. The most common method of frying is deep-fat frying, used worldwide due to its distinct flavor profile and sensory aspects, which leads to physio-chemical changes at both macro and micro levels. One of the major concerns with deep-fried foods is their high oil content, and a variety of metabolic disorders can be caused by overconsumption of these foods, including heart disease, obesity, and high cholesterol. Due to their enticing organoleptic properties with their delicious flavor, pleasing mouthfeel, and unique taste, making them irresistible, it is also responsible for undesirable and unacceptable characteristics for consumers. Oil absorption can be reduced by developing novel frying methods that limit the amount of oil in products, producing products with fewer calories and oil while maintaining similar quality, flavor, and edibility. In addition, different pretreatments and post-frying treatments are applied to achieve a synergistic effect. The transfer of mass and heat occurs simultaneously during frying, which helps to understand the mechanism of oil absorption in fried food. Researchers have discovered that prolonged heating of oils results in polar compounds such as polymers, dimers, free fatty acids, and acrylamide, which can alter metabolism and cause cancer. To reduce the oil content in fried food, innovative frying methods have been developed without compromising its quality which also has improved their effect on human health, product quality, and energy efficiency. The aim is to replace the conventional frying process with novel frying methods that offer fried food-like properties, higher nutritional value, and ease of use by replacing the conventional frying process. In the future, it might be possible to optimize frying technologies to substantially reduce fried foods' oil content. This review focuses on a detailed understanding of different frying techniques and attempts to focus on innovative frying techniques such as vacuum frying, microwave cooking, and hot-air frying that have shown a better potential to be used as an alternative to traditional frying.

Effect of moderate electric field voltage on the quality and heat transfer characteristics of potato strips during deep-frying process

The application of moderate electric field (MEF) on frying can influence the quality of fried products; however, the associated mechanism is unknown. This study investigated the effects of MEF voltage on the quality and surface heat transfer of potato strips fried with an MEF. With increasing MEF voltage, the moisture content, hardness, starch gelatinization rate, and shrinkage of the potato strips significantly increased (p < 0.05), while their oil content and brightness decreased (p < 0.05). The decrease in their oil content and brightness indicated improved crust formation, which reduced oil absorption. The potato strips fried under higher voltages exhibited lower oil contents and better microstructure than those fried under lower voltages. A possible mechanism comprised MEF increasing the heat transfer coefficient (h) between oil and potato strips, thereby accelerating crust formation; moreover, h values increased with MEF voltage. The results indicate the potential application of MEF in food frying.

Effects of Konjac Glucomannan on Oil Absorption and Safety Hazard Factor Formation of Fried Battered Fish Nuggets

The purpose of this study was to investigate the effects of konjac glucomannan (KGM) on oil absorption and the formation of safety hazard factors in fried battered fish nuggets by measuring advanced glycation end products (AGEs) and acrylamide contents. Other physicochemical properties were determined to explore the reason for oil absorption and formation of safety hazard factors. The acrylamide was found mainly in the crust. The addition of 0.8% KGM could significantly reduce the acrylamide content (p < 0.05). For the battered sample, the AGEs content was far lower than the unbattered. The addition of 0.8% KGM could significantly reduce the AGEs content in the inner layer (p < 0.05). The microstructure showed that the sample with 0.8% KGM had the most compact crust. The compact crust reduced oil and malondialdehyde contents. Combined with the other indicators, the inhibitory effect of 0.8% KGM on acrylamide was closely related with the decreased extent of oil oxidation and Maillard reaction in the samples with 0.8% KGM. The inhibitory effect of 0.8% KGM on AGEs might originate from its lower oil content.

Something to chew on: technological aspects for novel snacks

Snacks have accompanied people for a long time, meeting our needs for something fast and filling between meals. Societies and technologies have changed, and so have snacks, adapting to people's daily lives, concerns, and demands. Although traditional snacks, such as potato chips, are still ubiquitous and popular worldwide, there is not unanimity around them anymore, since many people have been looking for healthier snacks. Studies have been carried out to propose healthier snack options by changing their composition and/or techniques to produce them, minimizing contents of energy-dense components and/or maximizing the retention or bioavailability of nutrients. This mini-review presents the main trends on development of snacks and future perspectives. © 2021 Society of Chemical Industry.

Consumers' acceptance of the first novel insect food approved in the European Union: Predictors of yellow mealworm chips consumption

Climate and environmental-related challenges are high on the agenda of the European Union (EU). One priority is to redesign the existing food system into a more sustainable one, where the link between healthy people and a balanced environment is considered. The EU bets on the role of insect farming in supporting the transition toward healthier and future-proof diets. Following this orientation, we investigated consumers' attitude toward yellow mealworm chips (YMC) and identified the predictors of YMC consumption. The causal relationships between constructs were explored using the structural equation modeling (SEM) based on partial least squares (PLS) using SmartPLS software. The perceived lower environmental impact of YMC compared to meat was the most appreciated characteristic of YMC. The study identified five predictors of YMC consumption, among which the perceived characteristics of YMC have the strongest influence on the consumption probability. Against the expectations of the authors, disgust with the accidental encounter of insects in foods did not influence the probability of eating YMC. Age was another predictor of YMC consumption. It is known that food preferences and eating behaviors are mainly developed during childhood and tend to manifest in adult life. Consequently, it can be inferred that acceptance and preference for insect-based foods (IBF) should be stimulated from early childhood. Finally, practical implications are advanced as possible solutions to overcome the obstacles toward YMC consumption.

Effects of pulse electric field pretreatment on the frying quality and pore characteristics of potato chips

The main purpose of this work was to investigate the effect of pulsed electric field (PEF) treatment on the oil absorption capacity of potato chips, evaluated via changes to microstructure and pore characteristics. Our results showed that as electric field strength increased from 0 kV/cm (no pretreatment) to 5 kV/cm, the oil content of potato chips decreased by up to 20.6%. Furthermore, at higher the electric field strengths (5 ~ 20 kV/cm), most of the potato cell walls collapsed, and dense pores could be observed in the horizontal profile of the chips. Moreover, some smaller pores (10-50 nm) in the potato chips were disrupted and merged into larger pores (50-100 nm), thus increasing the total volume and average diameter of the pores, accelerating moisture evaporation and reducing oil absorption during frying. Our findings provide a novel perspective on the application of PEF towards the development of lower-fat and healthier fried foods.

Edible films and coatings – Not just packaging materials

Edible films and coatings (EFC) are macromolecular-based structures forming thin layers that are usually studied as tools to improve food stability, sometimes being considered as parts of both the packaging system and the food itself. However, EFC are not mere packaging materials, and sometimes they do not even play roles related to those of packaging. This graphical review summarizes possible roles of EFC, including primary packaging, keeping water activity gradients between food components, controlling mass transfer on food processing, carrying active components, or serving as sources of sensory appeal. EFC may even be designed in a way that two or more of those roles may be played simultaneously.

The influence of edible coatings and natural antioxidants on fresh-cut potato quality, stability and oil uptake after deep fat frying

The effect of four edible hydrocolloid coatings (carboxymethyl cellulose, chitosan, pectin and gum arabic) on fresh-cut potato's colour, pH and moisture content during storage was studied. Possibility of coating enrichment with natural olive leaf extract and sodium ascorbate was also evaluated. Coatings scored as the best ones straight after coating or during storage for 7 days at 10 ± 1 °C, were used for deep fat frying of potato. Chitosan was shown to cause significant decrease in pH and browning of potato strips. Pectin was classified as good coating alone but in combination with olive leaf extract showed lower quality parameters of fresh-cut samples compared to control. Only carboxymethyl cellulose and gum arabic itself or enriched with olive leaf extract or sodium ascorbate were shown not to affect colour, pH and moisture during storage. Moreover, these coatings significantly reduced fat content in deep fat fried potato strips, without influence on L*, b*, whiteness index (WI), and ΔE.

A summary of 2-, 3-MCPD esters and glycidyl ester occurrence during frying and baking processes

Monochloropropanediol (MCPD) esters and glycidyl esters (GE) are the process contaminants found in frying and baking, except the refining process. The free form MCPD and glycidol are released from their parent esters via lipase hydrolysis while they are carcinogen and genotoxic carcinogen, respectively. MCPD esters and GE are formed endogenously during vegetable oil refining process. Then, their concentration were experimented during subsequent food processing methods, especially frying and baking. This review discussed the occurrence of 2-, 3-MCPD esters and GE during frying and baking processes. Process temperature, process duration, presence of precursors, and their combined effects are highly related to MCPD esters and GE formations. An elevated temperature and processing time can increase the formation of these contaminants until an optimum rate and then followed by the decomposition. Also, other factors such as the presence of chloride ions, moisture, and partial acylglycerol can further facilitate MCPD esters and/or GE formation.

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Frying and baking trigger formation of MCPD esters and GE.

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MCPD esters and GE are formed endogenously during refining process.

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The concentration of MCPD esters and GE elevated during thermal processing.

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Temperature, process duration, and precursors cause MCPD esters and GE formations.

Characteristics of French Fries and Potato Chips in Aspect of Acrylamide Content—Methods of Reducing the Toxic Compound Content in Ready Potato Snacks

The reduction of toxic acrylamide content in potato snacks, i.e., French fries and potato chips, is necessary due to the adverse effects of this compound on the human body. Therefore, in the presented review paper, a detailed characterization of French fries and chips in terms of AA content and their organoleptic quality is included. Detailed information was also collected on the raw material and technological factors that affect the formation of acrylamide content, including methods and techniques affecting the reduction of the amount of this compound in potato snacks. The obligation to control the level of acrylamide in various food products (including fried potato snacks with a higher content of this compound), introduced in 2018, has mobilized manufacturers to seek solutions, while scientists conduct further intensive research on the possibility of reducing the level of AA or even eliminating its presence from products. Therefore, it is necessary to conduct such activities, especially, because potato French fries and potato chips are willingly consumed by younger and younger consumers.

Influence of food hydrocolloids on the structural, textural and chemical characteristics of low-fat banana chips

Banana chips are gaining popularity as a deep-fried product for its unique taste and flavour. This study is aimed to investigate the effect of hydrocolloids on oil absorption, physico-chemical and sensory properties of banana chips from two different varieties (var. Popoulu and var. Nendran), when fried at 180 °C for 3 min. The reduction in oil content was about 15%-35% and 19%-30% for hydrocolloid treated Popoulu and Nendran chips, respectively. The Free fatty acid content (FFA) of hydrocolloid treated banana chips was lower than that of untreated chips. The peroxide value (PV) values of all samples fell below 2 meq oxygen kg^-1. CMC pre-treated banana chips were crispier than other formulations on both the varieties. Microscopic analysis showed the improved cellular integrity without large void spaces in hydrocolloid treated banana chips. PCA analyses elucidated that variables such as physical appearance, colour, crispiness, after taste, overall acceptability contributed positively, whereas hardness and sogginess contributed negatively to the correlation among the variables. From the chemical and sensory attributes, 0.5% CMC treated Popoulu chips and 1% CMC treated Nendran chips is recommended to produce chips with lower oil content.

Effect of hydrocolloid coatings (Basil seed gum, xanthan, and methyl cellulose) on the mass transfer kinetics and quality of fried potato strips

In this research, the effect of different temperatures (160, 180, and 190 °C) and hydrocolloid coatings (Basil seed gum [BSG], xanthan gum [XG], methylcellulose [MC], BSG-XG, and BSG-MC mixtures) were investigated on the physicochemical properties (oil uptake, moisture loss, color, microscopic structure, activation energy, and texture), mass transfer kinetic of fried potato strips in deep-fat frying, and oil partitions using frying and postfrying cooling phase. An increase in frying time reduced the moisture content and hardness of potato strips; however, the oil content and color difference increased. The oil content in the coated samples had lower rates than that in the noncoated ones. The treated samples using BSG-xanthan mixture (50:50) and BSG had the lowest oil uptake at 0.13% and 0.14% Dry basis (d.b.), respectively. The maximum and minimum values of effective moisture diffusivity were measured in control and samples coated with BSG-XG and BSG, respectively. As frying temperature increased, the specific rate of oil uptake increased and the equilibrium oil content decreased. Overall, BSG-XG mixture-coated potato strips can be used as a promising product due to absorbing the lowest oil rate and being similar to the control in terms of organoleptic properties.

Review of knowledge to guide product development and breeding for sweetpotato frying quality in West Africa

This review provides background about sweetpotato in West Africa to identify the current importance and future potential of sweetpotato fried products in the region. We drew on global literature to consider current best practices and health aspects in addition to information from West Africa where frying in the form of large wedges or 'chunk fries' is predominant over other forms (i.e. chips (often referred to as crisps in England and the Commonwealth) and 'French fries'). Chunk fries are produced mostly by female-run microenterprises selling them as a filling snack to roadside and market customers. Boiling, drying and reconstituting in various foods, pounding and consumption of leaves as a vegetable are also important in the region. Further research will inform the development of a product profile for chunk fried sweetpotato and inform breeding strategies to improve sweetpotato for frying and other uses.