Deep-fried flavor: characteristics, formation mechanisms, and influencing factors

Characteristic volatiles fingerprints in olive vegetable stored at different conditions by HS-GC-IMS

The olive vegetable is popular food owing to its unique flavor. This study innovatively used headspace-gas chromatography-ion mobility spectrometry to evaluate olive vegetables' volatiles under different conditions. A total of 57 volatile compounds were determined from olive vegetables, including 30 aldehydes, 8 ketones, 5 alcohols, 2 esters, 8 hydrocarbons, 1 furans, 3 sulfur compounds. The PCA distinguished the olive vegetable stored at different conditions by volatiles. The gallery plot showed that olive vegetables stored at 4 °C for 21 d produced more limonene, which had a desirable fruity odor. The (E)-2-octenal, (E)-2-pentenal, (E,E)-2,4-heptadienal, 5-methylfurfural, and heptanal in fresh olive vegetables were lowest and increased with storage time. Furthermore, the change of volatiles was the least when the olive vegetable was stored at 0 °C. This study can provide theoretical bases for improving the flavor quality of olive vegetables and developing traditional food for standardized industrial production.

Evaluation of the effect of basil seed gum, tragacanth gum, pectin, and coating formulation with corn flour on oil absorption and sensory properties of watermelon rind chips

The current study aims to produce coated watermelon rind chips with the approach of reducing oil absorption and optimal use of waste and investigating its physicochemical, textural, and sensory characteristics. The effect of coating with basil seed gum, Tragacanth gum, pectin, and coating formulation with corn flour on oil absorption rate, moisture loss, and color of white skin slices of fried watermelon was studied. The results indicated that due to the controlling role of water in the amount of oil absorption, the amount of oil in all the samples coated with gum and corn flour was decreased compared to the samples coated with gum and the samples without coating. The pretreatment of osmotic dehydration reduces oil absorption in compared to fresh and blanched samples. The color changes in the sample with two pre-treatments of osmosis and blanching were less than other samples, as a result, the brightness of this sample was also higher than others. The lowest amount of oil absorption was observed in samples coated with basil gum and 0.5% and 1% corn flour (0.33 and 0.29, respectively). The highest amount of moisture loss during frying was related to the coated samples was observed with the combination of basil gum and corn flour (0.5%) and pectin and corn flour (2%). The highest level of antioxidant activity of the fried samples was related to the sample coated with 0.5% basil gum. Significant color changes were also observed in the coated samples.

Study on the Changes in Volatile Flavor Compounds in Whole Highland Barley Flour during Accelerated Storage after Different Processing Methods

The effect of heat processing on the flavor characteristics of highland barley flour (HBF) in storage was revealed by analyzing differences in volatile compounds associated with flavor deterioration in HBF using GC-MS identification and relative odor activity values (ROAVs). Hydrocarbons were the most abundant in untreated and extrusion puffed HBFs, while heterocycles were found to be the most abundant in explosion puffed, baked, and fried HBFs. The major contributors to the deterioration of flavor in different HBFs were hexanal, hexanoic acid, 2-pentylfuran, 1-pentanol, pentanal, 1-octen-3-ol, octanal, 2-butyl-2-octanal, and (E,E)-2,4-decadienal. Amino acid and fatty acid metabolism was ascribed to the main formation pathways of these compounds. Baking slowed down the flavor deterioration in HBF, while extrusion puffing accelerated the flavor deterioration in HBF. The screened key compounds could predict the quality of HBF. This study provides a theoretical basis for the regulation of the flavor quality of barley and its products.

Egg yolk phospholipids as an ideal precursor of fatty note odorants for chicken meat and fried foods: A review

Egg yolk phospholipids (PLs) have been demonstrated to generate large quantities of lipid-derived odorants, especially the fatty note odorants. Recently, egg yolk PLs have been successfully used in chicken meat and fried foods to improve aroma. This review comprehensively summarizes the properties of egg yolk PLs as precursors of fatty note odorants, including their classes, extraction, identification, oxidation, decomposition and odorant formation, applications, considerations and future prospects in the food industry. Most likely, phosphatidylcholine (PC) is the most abundant class in egg yolk PLs, and PC is more efficient than phosphatidylethanolamine in generating fatty note odorants; moreover, the predominant polyunsaturated fatty acid is linoleic acid, and its corresponding predominant hydroperoxide is 9-hydroperoxy-10,12-octadecadienoic acid during autoxidation, which is the precursor of 2,4-decadienals and 2,4-nonadienals, the key fatty note odorants. Therefore, egg yolk PLs could be an ideal precursor of fatty note odorants for chicken meat and fried foods.

Insight into the effect of traditional frying techniques on glycosylated hazardous products, quality attributes and flavor characteristics of grass carp fillets

This study aimed to evaluate the evolution of quality attributes, oxidation index, glycosylated hazardous products, aroma characteristics of grass carp fillets and their relationship under air-frying, roast-frying and pan-frying. With frying progressed, the level of carbonyl protein and lipid oxidation products increased significantly (following air-frying > pan-frying > roast-frying), and the latter decreased subsequently after 6 min. Fillets possessed by frying increased significantly N^ε-carboxymethyl-lysines (CML) and 5-hydroxymethylfurfural (5-HMF) levels, whose increment was pan-frying > air-frying > roast-frying. Compared to raw, eighty-seven volatiles were identified and the total concentrations of those increased gradually in air-frying, but then decreased up to 6 min in roast-frying and pan-frying. Furthermore, significant correlations between CML, TBARS and 5-HMF, quality attributes, oxidation index; volatiles (VIP and/or OAV > 1) and lipid oxidation index were obtained. Conclusively, fillets possessed by air-/roast-frying showed more lipid oxidation and alcohols/aldehydes, while pan-fried enriched CML and pyrazines.

Analysis of the Volatile Flavor Compounds of Pomegranate Seeds at Different Processing Temperatures by GC-IMS

This study sought to reveal the mechanism of flavor generation when pomegranate seeds are processed, as well as the contribution of volatile organic components (VOCs) to flavor formation. Gas chromatography–ion mobility spectrometry (GC-IMS), combined with relative odor activity (ROAV) and statistical methods, was used for the analysis. The results showed that 54 compounds were identified from 70 peaks that appeared in the GC-IMS spectrum. Then, the ROAV results showed 17 key volatile components in processing pomegranate seeds, and 7 flavor components with large differential contributions were screened out using statistical methods. These included γ-butyrolactone, (E)-3-penten-2-one (dimer), pentanal, 1-propanethiol, octanal, and ethyl valerate (monomer). It is suggested that lipid oxidation and the Maillard reaction may be the main mechanisms of flavor formation during the processing of pomegranate seeds. Furthermore, this study lays the experimental and theoretical foundations for further research on the development of flavor products from pomegranate seeds.

Exploring the Impact of α-Amylase Enzyme Activity and pH on Flavor Perception of Alcoholic Drinks

The introduction of a drink in the mouth and the action of saliva and enzymes cause the perception of basic tastes and some aromas perceived in a retro-nasal way. Thus, this study aimed to evaluate the influence of the type of alcoholic beverage (beer, wine, and brandy) on lingual lipase and α-amylase activity and in-mouth pH. It was possible to see that the pH values (drink and saliva) differed significantly from the pH values of the initial drinks. Moreover, the α-amylase activity was significantly higher when the panel members tasted a colorless brandy, namely Grappa. Red wine and wood-aged brandy also induced greater α-amylase activity than white wine and blonde beer. Additionally, tawny port wine induced greater α-amylase activity than red wine. The flavor characteristics of red wines due to skin maceration and the contact of the brandy with the wood can cause a synergistic effect between beverages considered "tastier" and the activity of human α-amylase. We can conclude that saliva-beverage chemical interactions may depend on the saliva composition but also on the chemical composition of the beverage, namely its constitution in acids, alcohol concentration, and tannin content. This work is an important contribution to the e-flavor project, the development of a sensor system capable of mimicking the human perception of flavor. Furthermore, a better understanding of saliva-drink interactions allow us to comprehend which and how salivary parameters can contribute to taste and flavor perception.

The Establishment of Evaluation Models for the Cooking Suitability of Different Pork Muscles

Pork is the main meat consumed by Chinese people. In this study, the sensory quality of four muscles (loin, shoulder, belly, and ham) under three cooking methods (boiling, scalding, and roasting) was examined, and the edible quality and nutritional quality of fresh meat were determined at the same time. Principal component analysis, cluster analysis, correlation analysis, and analysis of the coefficient of variation were used to determine key quality indicators, from which comprehensive quality evaluation equations were established. The results showed that, when meat was boiled, the comprehensive quality evaluation model was Y=0.1537X1+0.1805X2+0.2145X3+0.2233X4+0.2281X5 (X₁~X₅ are a*, fat, odor, tenderness, and flavor, respectively) and the most suitable muscle was belly; when meat slices were scalded in a hot pot, the comprehensive quality evaluation model was Y=0.1541X1+0.1787X2+0.2160X3+0.2174X4+0.2337X5 (X₁~X₅ are a*, fat, odor, tenderness, and flavor, respectively) and the most suitable muscle was belly; when meat was roasted, the comprehensive quality evaluation model was Y=0.1539X1+0.1557X2+0.1572X3+0.1677X4+0.1808X5+0.1845X6 (X₁~X₆ are flavor, marbling, elasticity, cooked flesh color, tenderness, and flesh color, respectively), and the most suitable muscles were belly and shoulder.

Analysis of volatile compounds and flavor fingerprint in hairtail (Trichiurus lepturus) during air-drying using headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS)

In the present study, changes in volatile compounds during processing were analyzed using the headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS), to investigate the generation of aroma in hairtails (Trichiurus lepturus) during air-drying. Physicochemical indices, such as moisture content and thiobarbituric acid reactive substances (TBARS), were also detected. Flavor fingerprints were studied and developed to distinguish the samples of fresh hairtails (0 day) from air-dried hairtails (2 and 4 days). A total of 75 volatile organic compounds (VOCs) were identified in hairtails, in which alcohols, aldehydes, ketones, and esters were the principal contributors to the formation of the overall flavor of hairtails during air-drying. Seven flavor compounds (ethanol, 3-methyl-1-butanol, 1-pentanol, hexanal, octanal, benzaldehyde, and 3-methylbutanal), two flavor compounds (acetoin and dimethyl sulfide), and eight flavor compounds (1-hexanol, 1-octen-3-ol, nonanal, heptanal, 2-heptanone, ethyl acetate, trimethylamine, and ammonia) were identified in 0, 2, and 4 air-dried hairtails as biomarkers, respectively. The results showed that HS-GC-IMS could detect VOCs in different air-dried hairtails rapidly and comprehensively.

Unraveling the Thermal Oxidation Products and Peroxidation Mechanisms of Different Chemical Structures of Lipids: An Example of Molecules Containing Oleic Acid

Lipid structures affect lipid oxidation, causing differences in types and contents of volatiles and nonvolatiles in various foods. In this study, the oxidation differences of monoacylglycerol (MAG), triacylglycerol (TAG), phosphatidylethanolamine (PE), and phosphatidylcholine (PC) with oleoyl residues and oleic acid (FA) during thermal treatment were investigated. Volatiles and nonvolatiles were monitored by gas chromatography-mass spectrometry and ultrahigh-performance liquid chromatography-Q-Exactive HF-X Orbitrap Mass Spectrometer, respectively. The results showed that the structures of MAG and TAG could delay the chain initiation reaction. The polar heads of PC and PE remarkably influenced the oxidation rate and the formation of the oxidation products probably due to the hydrogen bonds formed with free radicals. Among the volatile oxidation products, aldehydes, acids, and furans with eight or nine carbon atoms accounted for the majority in FA, MAG, TAG, and PC samples, but PE samples mainly generated ketones with nine or 10 carbon atoms. The formation of nonvolatile products in TAG samples possessed significant stage-specific changes. Fatty acid esters of hydroxy fatty acids were only produced in the free fatty acid oxidation model. The activity of chemical bonds participating in the truncation reaction decreased to both sides from the double bond position.

Study on the physicochemical and flavor characteristics of air frying and deep frying shrimp (crayfish) meat

This study aimed to compare the changes in the quality characteristics of air-fried (AF) shrimp meat and deep-fried (DF) shrimp meat at different frying temperatures (160, 170, 180, 190°C). Results showed that compared with DF, the moisture and fat content of air-fried shrimp meat (AFSM) was lower, while the protein content was higher. At the same frying temperature, the fat content of the AFSM was 4.26-6.58 g/100 g lower than that of the deep-fried shrimp meat (DFSM). The smell of the AFSM and DFSM was significantly different from that of the control group. The results of the electronic tongue showed that each of the two frying methods had its flavor profile. Gas chromatography-ion mobility spectrometry (GC-IMS) identified 48 compounds, and the content of volatile compounds detected in AFSM was lower than that in DFSM. Among them, the highest level of volatile compound content was found in the DF-190. E-2-pentenal, 2-heptenal (E), and methyl 2-methyl butanoate were identified only in DFSM. In addition, a total of 16 free amino acids (FAAs) were detected in shrimp meat. As judged by sensory evaluation, the AFSM at 170°C was the most popular among consumers.

Investigation of volatile flavor compounds and characterization of aroma-active compounds of water-boiled salted duck using GC-MS-O, GC-IMS, and E-nose

To clarify the characteristic aroma substances of water-boiled salted duck (WSD), headspace-gas chromatography-mass spectrometry-olfactometry (HS-GC-MS-O), gas chromatography-ion mobility spectrometry (GC-IMS) combined with an electronic nose (E-nose) were used to analyze the volatile flavor profile of three types of WSD (containing four samples). Thirty-one and fifty volatile flavor components were identified by GC-MS and GC-IMS, including aldehydes, alcohols, esters, ketones, hydrocarbons, and others. The characteristic aroma compounds of WSD, including pentanal, hexanal, heptanal, octanal, nonanal, (E)-2-octenal, benzaldehyde, (E)-2-nonenal, decanal, 1-octen-3-ol, 1-octanol, 1-pentanol, ethyl acetate, d-limonene, and 2-pentylfuran, were confirmed by GC-O, odor activity values (OAVs), and aroma-recombination and omission experiments. The aroma description of these aroma-active compounds can be divided into 6 categories, namely, "fruity", "mushroom", "fat", "sweet", "faint scent" and "potato, scorch" aromas. The difference between samples was mainly caused by the differential volatile compounds, followed by the identification method.

An Evaluation Model for the Quality of Frying Oil Using Key Aldehyde Detected by HS-GC/MS

To establish a practical model for evaluating the oxidation of frying oil using aldehydes, the aldehydes of 10 commercial oils during frying at 180 °C were identified using headspace-gas chromatography/mass spectrometry, and the changes of common aldehydes and their correlation with carbonyl values (CV) were analyzed. The results showed that the total peak area of aldehydes increased significantly with heating time, which was related to the fatty acid and tocopherol contents of the oils. There were four common aldehydes with different trends during frying, namely, pentanal, hexanal, (E)-hept-2-enal, and nonanal. Moreover, pentanal with a high correlation with CV was selected as the quality evaluating index of frying oil due to its stable accumulation over time. Based on the linear fitting relationships between CV and pentanal, as well as the initial content ratio of linoleic acid to palmitic acid and total tocopherols in oils, a predictive model was established for evaluating the quality of frying oils with high precision and non-reagent by using mass spectrometry. In summary, this work provides theoretical support for using aldehyde as the quality evaluation index of frying oil and provides a new idea for evaluating oil deterioration from the perspective of volatile compounds.

Influence of thermal processing on the quality of hawthorn: quality markers of heat-processed hawthorn

Hawthorn and its derived products are used worldwide as foods as well as complementary medicine. During the preparation of hawthorn, heating and thermal processing are frequently reported. The thermal processing will change the medicinal purposes and modify the efficacy of hawthorn. However, details including the chemical profile shifting and quality markers of heat-processed hawthorn have not been well understood. In the paper, we analyzed the hawthorn samples processed at different temperatures and different times by ultraviolet visible absorption spectrum and LC-MS technologies combined with multivariate statistical analysis. It was revealed for the first time that thermal processing could greatly change the ultraviolet visible absorption spectra and chemical profiles of hawthorn even with heat treatment at 130°C for 10 minutes. And the ultraviolet visible absorption spectrum, especially the ratio value (R_{A500 nm/400 nm} ), was a descriptive and qualitative indicator of heating degree for the thermal processing at the macroscopic level. Several components, such as hyperoside, chlorogenic acid, quercetin and apigenin, decreased or increased in content during the processing, and they could be utilized as the chemical quality markers. The proposed quality markers for heat-processed hawthorn will be helpful for further optimizing the processing conditions of hawthorn. This article is protected by copyright. All rights reserved.

Gender and socio-economic stratification of ultra-processed and deep-fried food consumption among rural adolescents: A cross-sectional study from Bangladesh

Background

Although consumption of ultra-processed and deep-fried foods among adolescents is a global health concern, little is known about its gender and socio-economic stratification in rural settings of low- and middle-income countries. We, thus, aimed to describe ultra-processed and deep-fried food consumption among rural adolescents by gender and socio-economic factors, and to explore their relative importance in shaping consumption.

Methods

This cross-sectional study drew on data from a household survey in Matlab, a rural sub-district in Bangladesh. The analytic sample comprised 2463 adolescents. We assessed consumption of four ultra-processed food groups: ready-to-eat or “instant” foods; confectionery, sweets and similar packaged products; savory snacks; sugar-sweetened beverage; and of deep-fried foods with a 24-hour, qualitative recall. Asset scores were constructed. Proportion of consumption was calculated and compared by gender and household wealth. Logistic regression models were fitted to isolate socio-demographic variables associated with consumption.

Results

Approximately 83% (81.5–84.4) adolescents consumed at least one ultra-processed or deep-fried item. Confectioneries were the most consumed (53.5%), whereas sugar-sweetened beverage was the least consumed (12%) group. Boys had greater odds of consumption than girls for all food groups. The association was strongest for sugar-sweetened beverage (adjusted odds ratio = 2.57; 95% CI: 1.97, 3.37), followed by deep-fried foods (adjusted odds ratio = 1.96; 95% CI: 1.66, 2.32) and ready-to-eat foods (adjusted odds ratio = 1.85; 95% CI: 1.45, 2.38). Belonging to the richest households was associated with ready-to-eat food consumption (adjusted odds ratio = 1.55; 95% CI: 1.12, 2.16). Adolescents with higher educational attainment had lower odds of consuming sugar-sweetened beverage (adjusted odds ratio = 0.73; 95% CI: 0.54, 0.98).

Conclusion

Consumption of packaged confectioneries, savory snacks, and deep-fried foods appeared common, while SSB consumption was relatively low. Role of gender was pre-eminent as consumption was more likely among boys across the food groups. This may disproportionately expose them to the risk of diet-related non-communicable diseases.

Effects of Frying Conditions on Volatile Composition and Odor Characteristics of Fried Pepper (Zanthoxylum bungeanum Maxim.) Oil

Fried pepper (Zanthoxylum bungeanum Maxim.) oil (FPO) is widely used in Chinese cuisine because of its unique aroma. To investigate the effects of different frying temperatures and different frying times on the volatile composition and odor characteristics of FPOs, descriptive sensory analysis (DSA), solvent-assisted flavor evaporation–gas chromatography–mass spectrometry (SAFE–GC–MS) and electronic nose (E-nose) were used to analyze the FPOs (FPO1–FPO4 represented the pepper oil fried at 110 °C, 120 °C, 130 °C, and 140 °C; FPO5–FPO7 represented the pepper oil fried for 10 min, 20 min and 30 min). The results showed that FPO3 and FPO6 had strong citrus-like and floral aromas and exhibited significant advantages in sensory attributes. A total of 46 volatile compounds were identified by SAFE–GC–MS; among them, FPO3 and FPO6 had a higher volatile compound content. β-Caryophyllene was detected in only FPO3 and FPO6; linalool was higher in FPO3 and FPO6, which might cause them to exhibit stronger floral and citrus-like aromas. The presence of (2E,4E)-2,4-decanedienal would be one of the reasons for the strong fatty aroma exhibited in FPO4 and FPO7. FPO3 and FPO6 were associated with citrus-like and floral aromas by partial least squares regression (PLSR) analysis, which agreed with the sensory evaluation results.

Comparative analysis of aroma compounds in French fries and palm oil at three crucial stages by GC/MS-olfactometry, odor activity values, and aroma recombination

BACKGROUND

Flavor is a key element affecting the popularity of French fries (FFs). When oil is heated, the changes in oil quality can affect the flavor of the food directly.

RESULTS

The flavor of FFs showed three crucial stages: the break-in (3.0% to 6.8% of total polar compounds (TPC)), optimum (7.0% to 19% of TPC), and degrading (above 19.5% of TPC) stages. To distinguish the key aroma compounds in the three stages, the FFs, prepared in palm oil (PO) at TPC of 3.0% (FF3), 7.5% (FF8), 19.5% (FF20), and their relevant oils (PO3, PO8, PO20), were selected for molecular sensory science analysis. The results indicated that the concentration of (E, E)-2,4-decadienal linked with the deep-fried odor was low in FF3, which led to a lower sensory score in the FF3 sample. The FF8 sample had a high (E, E)-2,4-decadienal content and received a high sensory score. The FF20 sample possessed high hexanoic acid, heptanoic acid (sweaty odor), benzaldehyde (stale odor), octanoic acid (sweaty odor), (E)-2-undecenal (fatty odor), and trans-4,5-epoxy-(E)-2-decenal (metallic odor) content, thus leading to FFs having an undesirable flavor and PO20 showed high hexanoic acid and heptanoic acid content, contributing to a lower sensory score in PO20.

CONCLUSION

The FFs' flavor became undesirable when TPC was above 19.5% due to significant influences of some off-flavor compounds. It is therefore essential to prevent the generation of rancid substances to prolong the optimum stage during frying. © 2021 Society of Chemical Industry.

Characterization of Taste Compounds and Sensory Evaluation of Soup Cooked with Sheep Tail Fat and Prickly Ash

Sheep tail fat and prickly ash play an important role in improving the umami taste of mutton soup. In this work, the effects of prickly ash on key taste compounds in stewed sheep tail fat soup were investigated. Results showed that the taste intensity of sheep tail fat soup cooked with 0.2% prickly ash increased significantly. The concentration of organic acids and free amino acids in sheep tail fat soup significantly increased with the addition of prickly ash. The concentration of succinic acid (2.637 to 4.580 mg/g) and Thr (2.558 to 12.466 mg/g) increased the most among organic acids and amino acids, respectively. Spearman’s correlation analysis elucidated that seven taste compounds were positively correlated (correlation coefficient > 0.7) with the overall taste intensity of the soup sample including Thr, Asp, oxalic acid, lactic acid, citric acid, succinic acid, and ascorbic acid. Additional experiments and quantitative descriptive analysis further confirmed that Asp, lactic acid and citric acid were the key taste compounds to improve saltiness and umami taste in sheep tail fat soup with prickly ash.

Dissecting grilled red and white meat flavor: Its characteristics, production mechanisms, influencing factors and chemical hazards

Meat flavor is composed of a complex mixture of volatile compounds developed as a result of heat driven multi-directional reactions. Typical reactions include Maillard reaction, lipid oxidation, as well as nitrogenous compounds degradation. Such complex flavor is characterized by a rich variety of volatile species, and to strongly influence consumer's preference. The objective of this review is to holistically dissect the flavor characteristic for cooked meat products with special emphasis on grilling and the factors that affect their production to ensure best quality and or safety levels. The review also highlights different analytical techniques used for the detection of flavor compounds in grilled meat. This comprehensive literature research critically analyze grilled flavor derived from heat mediated reactions, with a special emphasis on key flavors or hazard chemicals and their production mechanism. The various influencing factors i.e., grilling temperature, meat, food components, animal ante-mortem factors and food additives are summarized.

Characterization of the Key Aroma Constituents in Fried Tilapia through the Sensorics Concept

The object of this study was tilapia fish that were fried in soybean oil. Volatile compounds were extracted from the fish by ASE-HVE and were studied by GC-O-MS and the AEDA analysis method. A total of 30 aroma compounds were initially determined, and these compounds contribute to the aroma of fried tilapias. The key volatile compounds in fried tilapia were quantitatively analyzed by GC-MS, and the volatile compounds in soybean-fried tilapia were studied by flavor recombination and deletion experiments. Trimethylamine, hexanal, 2,3-dimethylpyrazine, dimethyl trisulfide, trans-2-octenal, 2,3-dimethyl-5-ethylpyrazine, (E)-2-nonenal, 2-propyl-pyridine, and (E,E)-2,4-decadienal were finally determined to be the key volatile compounds in soybean-fried tilapia.

Glycine and serine markedly eliminate methylglyoxal in the presence of formaldehyde via the formation of imidazole salts

l-glycine and l-serine are the building blocks of proteins and exhibit various biological activities. This work found that l-glycine and l-serine show low scavenging capacity for methylglyoxal at moderate conditions (pH 7.0, 37 °C). However, they efficiently eliminate methylglyoxal and formaldehyde when the two aldehydes co-exist, via generation of imidazole salt, a compound formed by one molecule of methylglyoxal and formaldehyde, and two molecules of amino acids. The imidazole salts were identified in biscuits and fried potato crisps. Moreover, the formation of imidazole salts greatly decreased the cytotoxicity of their precursors, methylglyoxal and formaldehydes. This finding suggests that glycine and serine can be used to scavenge these two harmful aldehydes both after intake and during food processing.

Effects of Repeated Heating on Fatty Acid Composition of Plant-Based Cooking Oils

Several polyunsaturated fatty acids are considered to have beneficial health effects, while saturated fatty acids and industrial trans fatty acids (TFAs) are linked to negative health consequences. Given the increased formation of TFAs during heating, many studies already investigated compositional changes in oils after prolonged heating or at extremely high temperatures. In contrast, our aim was to measure changes in fatty acid composition and in some health-related indices in edible oils after short-time heating that resembles the conventional household use. Potatoes were fried in palm, rapeseed, soybean, sunflower and extra virgin olive oils at 180 °C for 5 min, and samples were collected from fresh oils and after 1, 5 and 10 consecutive heating sequences. Regardless of the type of oil, the highest linoleic acid and alpha-linolenic acid values were measured in the fresh samples, whereas significantly lower values were detected in almost all samples following the heating sequences. In contrast, the lowest levels of TFAs were detected in the fresh oils, while their values significantly increased in almost all samples during heating. Indices of atherogenicity and thrombogenicity were also significantly higher in these oils after heating. The present data indicate that prolonged or repeated heating of vegetable oils should be avoided; however, the type of oil has a greater effect on the changes of health-related indices than the number of heating sequences.

Effect of Psidium guajava leaves extracts on thermo-lipid oxidation and Maillard pathway born food toxicant acrylamide in Indian staple food

Deep frying of food is a common practice that leads to the formation of lipid oxidation products. These lipid oxidation products have a role in the Maillard reaction, which ultimately leads to the formation of cancer-causing and neurotoxic substance acrylamide. In this regard, the Psidium guajava leaves extract-treated sunflower oil on oxidative stability and acrylamide content in pooris a popular deep-fried staple food in India were studied and compared with synthetic antioxidant butylated hydroxytoluene (BHT) till four frying cycles. P. guajava leaves contain 173.33 ± 1.95 mg GAE/g extract total phenolic content and 20.43 ± 0.25 mg RUE/g extract total flavonoid content. Some of the phytochemicals in the extract were identified and quantified by HPTLC. P. guajava leaves extract (1 g) contained 0.039 mg gallic acid, 0.196 mg rutin, 0.021 mg naringenin, 0.059 mg ferulic acid. The IC50 values for guava leaves extract, BHT, and ascorbic acid were 61.4, 30.4, 26.6 µg/mL, respectively. The peroxide and p-anisidine values indicated that P. guajava leaves extract inhibited lipid oxidation and provided oxidative stability. Pooris fried in P. guajava leaves extract-treated, BHT treated sunflower oil contained a lower acrylamide than pooris fried in control sunflower oil.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at (10.1007/s13197-021-04984-y).

Schemes for enhanced antioxidant stability in frying meat: a review of frying process using single oil and blended oils

Deep-fried meat products are widely popular. However, harmful compounds produced by various chemical reactions during frying have been shown to be detrimental to human health. It is of great necessity to raise practical suggestions for improving the oxidation problem of frying oils and frying conditions in some aspects. Vegetable oils are not as thermally stable as saturated fats, and blended oils have higher thermal stability than single oil. In this review, we discussed the oxidation problems frying oils and meats are subject to during frying, starting from the oil oxidation mechanism, the effects of different oils and fats on the quality of different fried meats under different conditions were concluded to alleviate the oxidation problem, to highlight the necessity of applying blended oils for frying, and effective antioxidants added to frying oils are also introduced, that would provide more convenient and practical options for obtaining higher quality of fried meat products and offer better understanding of the potential of blended frying oils for frying meat products.

Effect of oilseed roasting on the quality, flavor and safety of oil: A comprehensive review

Roasting is widely applied in oil processing and employs high temperatures (90-260 °C) to heat oilseeds evenly. Roasting improves the extraction yield of oil by the generation of pores in the oilseed cell walls, which facilitates the movement of oil from oilseed during subsequent extraction. It also affects the nutritional value and palatability of the prepared oil, which has attracted consumers' attention. An appropriate roasting process contributes to better extraction of bioactive compounds, particularly increasing the total polyphenol content in the oil. Correspondingly, extracted oil exhibits higher antioxidant capacity and oxidative stability after roasting the oilseeds due to better extraction of endogenous antioxidants and the generation of Maillard reaction products. Furthermore, roasting process is critical for the formation of aroma-active volatiles and the improvement of desired sensory characteristics, so it is indispensable for the production of fragrant oil. However, some harmful components are inevitably generated during roasting, including oxidation products, polycyclic aromatic hydrocarbons, and acrylamide. Monitoring and controlling the concentrations of harmful compounds in the oil during the roasting process is important. Therefore, this review updates how roasting affect the quality and safety of oils and provides useful insight into regulation of the roasting process based on bioactive compounds, sensory characteristics, and safety of oils. Further research is required to assess the nutritional value and safety of roasted oils in vivo and to develop a customized roasting process for various oilseeds to produce good-quality oils.

Kinetics of Moisture Loss and Oil Absorption of Pork Rinds during Deep-Fat, Microwave-Assisted and Vacuum Frying

The fat content of fried pork rinds is high, and alternative frying helps reduce the oil content and maintain their texture and taste. Different frying methods such as microwave-assisted, traditional deep frying and vacuum frying on the breaking force, color, microstructure, water loss and oil absorption attributes of fried pork rinds were evaluated in this study. The fat content of microwave-assisted and vacuum-fried pork rinds was lower (24.2 g/100 g dry weight basis (db) and 17.1 g/100 g db, respectively) than that (35.6 g/100 g db) of traditional deep-fat frying. Non-uniform, holy and irregular surface microstructures were obtained by vacuum frying due to rapid mass transfer at low pressure. The first-order kinetic models of water loss and oil absorption of traditional and microwave-assisted frying of pork rinds were established. Microwave frying caused a faster moisture loss rate, shorter frying time and lower pork rind oil content, makes it an attractive substitute for traditional deep-fat frying.

Comparative characterization of key odorants of French fries and oils at the break-in, optimum, and degrading frying stages

Flavor is a significant factor determining the popularity of French fries (FFs). The frying process of soybean oil (SO) showed three obvious stages-break-in, optimum, and degrading. Further, in order to distinguish the key aroma compounds in each stage, the FFs prepared in SO with total polar compounds (TPC) of 6.5% (FF7), 16.37% (FF16), and 26.5% (FF27), and their corresponding oils (SO7, SO16, SO27) were chosen for sensory-directed analysis. In the break-in stage (6.50-13.50% of TPC), the flavor of the FFs was light and undesirable due to the lower content of (E,E)-2,4-decadienal. Then at the optimum stage (15.43-22.70% of TPC), the FFs obtained a higher sensory score, mainly owing to the increase of (E,E)-2,4-decadienal with a strong, deep-fried odor. However, in the degrading stage (over 22.70% of TPC), high level of four acids (hexanoic, heptanoic, octanoic, and nonanoic acid), benzeneacetaldehyde and trans-4,5-epoxy-(E)-2-decenal resulted in flavor deterioration in FF27.

The relationship between flavor formation, lipid metabolism, and microorganisms in fermented fish products

Traditional fermented fish products are favored due to their unique flavors. The fermentation process of fish is accompanied by the formation of flavor substances through a complex metabolic reaction of microorganisms, especially lipolysis and lipid oxidation. However, it is difficult to precisely control the reaction of microorganisms during the fermentation process in modern industrial production, and fermented fish products have lost their traditional characteristic flavors. The purpose of this review is to summarize the different kinds of fermented fish, core microorganisms in it, and flavor formation mechanisms, providing guidance for industrial cultural starters. Future research on the flavor formation mechanism is necessary to confirm the relationship between flavor formation, lipid metabolism, and microorganisms to ensure stable flavor and safety, and to elucidate the mechanism directly toward industrial application.

Influence of Oil Types and Prolonged Frying Time on the Volatile Compounds and Sensory Properties of French Fries

In order to study the flavor of French fries (FFs) prepared in different frying oils, we identified and compared the volatiles of FFs fried in high-oleic sunflower oil (HSO), sunflower oil (SO), linseed oil (LO), and palm oil (PO) during prolonged 24 h frying time. 47 different kinds of volatiles were presented, and aldehydes were the most abundant compounds. The FFs prepared in SO were rich in alkadienals, especially the (E, E)-2,4-decadienal, thus inducing the highest deep-fried odor. The content of alkenals was higher in FFs prepared in HSO, among which (E)-2-nonenal and 2-undecenal provided the undesirable oily flavor. Whereas, FFs prepared in PO were rich in alkanals, and showed an undesirable green aroma because of hexanal. Besides, the aldehydes in FFs fried in LO were the least with more undesirable flavor substances (e.g. (E, E)-2,4-heptadienal). In addition, except for the FFs fried in LO, the aldehydes in other FFs showed an increasing trend. While, the volatiles from the Maillard reaction (e.g. pyrazines) showed no clear pattern. Meanwhile, frying process had optimum frying window (approximately 12 h with total polar compounds content of 14.5%-22.2% in different oils), and the French fries prepared in this period obtained higher flavor score. Therefore, the comparison related to volatiles of FFs provided a basis for the flavor control to a certain extent.

Contribution of starch to the flavor of rice-based instant foods

Increased consumption of instant foods has led to research attention, especially rice-based instant foods. Starch, one of the most important components of rice, significantly affects food quality. However, the mechanisms by which starch contributes to rice-based instant foods flavor are poorly understood in many cases. The review aims to describe the common mechanisms by which starch contributes to food flavor, including participating in flavor formation, and affecting flavor release throughout starch multiscale structure: particle morphology, crystal structure, molecular structure. Five specific examples of rice-based instant foods were further analyzed to summarize the specific contribution of starch to flavor, including instant rice, fermented rice cake, rice noodles, fried rice, and rice dumplings. During foods processing, reducing sugars produced by heating or enzymatic hydrolysis of starch participate in Maillard reaction, caramelization and thermal degradation, which directly or indirectly affect the formation of flavor compounds. In addition, adsorption by granules, encapsulation by retrograded V-type crystal, and controlled release by starch gel all contribute to rice-based instant food flavor qualities. These mechanisms jointly contribute to flavor compounds formation and release. Proper theoretical application and improved processing methods are needed to promote the high-quality, mechanization, and automation of rice-based instant foods production.