Influence of pH and Composition on Nonenzymatic Browning of Shelf-Stable Orange Juice during Storage

Changes in phenolic compounds of Phyllanthus emblica juice during different storage temperature and pH conditions

The aim of this experiment was to investigate the effect of storage temperature and pH on phenolic compounds of Phyllanthus emblica juice. Juice was stored at different temperatures and pH for 15 days and sampled on 2-day intervals. The browning index (BI, ABS420 nm), pH, centrifugal precipitation rate (CPR), and phenolic compounds were evaluated. The results showed 4°C and pH 2.5 could effectively inhibit browning and slow down pH drop of P. emblica juice. The result of orthogonal partial least square-discriminant analysis showed P. emblica juice stored at 4°C and pH 2.5 still had a similar phenolic composition, but at 20°C, 37°C, and pH 3.5, the score plots were concentrated only in the first 3 days. Additionally, gallic acid (GA) and ellagic acid (EA) were screened out to be the differential compounds for browning of P. emblica juice. The contents of GA, epigallocatechin (EGC), corilagin (CL), gallocatechin gallate (GCG), chebulagic acid (CA), 1,2,3,4,6-O-galloyl-d-glucose (PGG), and EA were more stable at 4°C and pH 2.5. Overall, during storage at 4°C and pH 2.5, it could inhibit the increase of GA and EA and decrease of CL, GCG, CA, and PGG, whereas EGC did not show significant difference between storage conditions. The CPR was higher at 4°C, while pH 2.5 could reduce the CPR. In conclusion, in order to maintain stability of phenolic compounds and extended storage period, the P. emblica juice could be stored at low temperature and adjust the pH to increase the stability of juice system.

Effects of different hot-air drying methods on the dynamic changes in color, nutrient and aroma quality of three chili pepper (Capsicum annuum L.) varieties

The effects of constant and variable temperature hot-air drying methods on drying time, colors, nutrients, and volatile compounds of three chili pepper varieties were investigated in this study. Overall, the variable temperature drying could facilitate the removal of water, preserve surface color, and reduce the loss of total sugar, total acid, fat and capsaicin contents. Electronic-nose (E-nose) and gas chromatography-ion mobility spectroscopy (GC-IMS) analyses found that aldehydes, ketones, alcohols and esters contributed to the aroma of chili peppers. The drying process led to an increase in acids, furans and sulfides contents, while decreasing alcohols, esters and olefins levels. In addition, the three chili pepper varieties displayed distinct physical characteristics, drying times, chromatic values, nutrients levels and volatile profiles during dehydration. This study suggests variable temperature drying is a practical approach to reduce drying time, save costs, and maintain the commercial appeal of chili peppers.

Mechanism of Dihydromyricetin-Induced Reduction of Furfural Derived from the Amadori Compound: Formation of Adducts between Dihydromyricetin and Furfural or Its Precursors

Dihydromyricetin (DMY) was employed to reduce the yield of furfural derived from the Amadori rearrangement product of l-threonine and d-xylose (Thr-ARP) by trapping Thr-ARP, 3-deoxyxyosone (3-DX), and furfural to form adducts. The effect of different concentrations of DMY at different pH values and temperatures on the reduction of furfural production was studied, and the results showed that DMY could significantly reduce furfural production at higher pH (pH 5-7) and lower temperature (110 °C). Through the surface electrostatic potential analysis by Gaussian, a significant enhancement of the C6 nucleophilic ability at higher pH (pH ≥ 5) was observed on DMY with hydrogen-dissociated phenol hydroxyl. The nucleophilic ability of DMY led to its trapping of Thr-ARP, 3-DX, and furfural with the generation of the adducts DMY-Thr-ARP, DMY-3-DX, and DMY-furfural. The formation of the DMY-Thr-ARP adduct slowed the degradation of Thr-ARP, caused the decrease of the 3-DX yield, and thereby inhibited the conversion of 3-DX to furfural. Therefore, DMY-Thr-ARP was purified, and the structure was identified by nuclear magnetic resonance (NMR). The results confirmed that C6 or C8 of DMY and carbonyl carbon in Thr-ARP underwent a nucleophilic addition reaction to form the DMY-Thr-ARP adduct. In combination with the analysis results of Gaussian, most of the DMY-Thr-ARP adducts were calculated to be C6-DMY-Thr-ARP. Furthermore, the formation of DMY-furfural caused furfural consumption. The formation of the adducts also shunted the pathway of both Thr-ARP and 3-DX conversion to furfural, resulting in a decrease in the level of furfural production.

Non-enzymatic browning of a composite puree of Choerospondias axillaris, snow pear, and apple: kinetic modeling and correlation analysis

Choerospondias axillaris, snow pear, and apple composite fruit puree can be affected by non-enzymatic browning during storage decreasing the market value of the product. This study aimed to explore, using kinetic methods, the effects of non-enzymatic precursors (polyphenols and ascorbic acid) and intermediates (5-hydroxymethylfurfural) on fruit puree stored at 4 °C for 35 days. The results showed that ascorbic acid fitted the first-order reaction model, while the 5-hydroxymethylfurfural was consistent with the complex reaction model. Furthermore, the 5-hydroxymethylfurfural content was 1.53 ± 0.18 mg/L, (corresponding to an increase of 565%), and the ascorbic acid content was 0.88 ± 0.22 mg/100 g, (corresponding to a decrease of 98.5%). The results also demonstrated a change in the titratable acid, soluble solids, and pH of the fruit puree. Finally, the correlation results revealed a significant correlation between non-enzymatic browning and 5-hydroxymethylfurfural, titratable acid, and pH (p < 0.05). Overall, the results suggest that the Maillard reaction could be responsible for the non-enzymatic browning of fruit purees during storage.

Simultaneously Enhanced Formation of Pyrazines and Furans during Thermal Degradation of the Glycyl-l-glutamine Amadori Compound by Selected Exogenous Amino Acids and Appropriate Elevated Temperatures

The Amadori compound of glucose and glycyl-l-glutamine (Gly-Gln-ARP) was prepared and characterized by UPLC-MS/MS and NMR. Gly-Gln-ARP could be thermally degraded into Gly-Gln and other secondary reaction products like glycyl-l-glutamic acid and its ARP via deamidation. The thermal processing temperature exerted a tremendous influence on the flavor formation of ARP. Furans were mainly formed at 100 °C, while an elevated temperature of 120 °C facilitated the massive accumulation of α-dicarbonyl compounds through the retro-aldolization of deoxyglucosone, and then increased the formation of pyrazines. The extra-added amino acids further promoted the formation of pyrazines at 120 °C, especially Glu, Lys, and His, further increasing the total concentration of pyrazines to 457 ± 6.26, 563 ± 65.5, and 411 ± 59.2 μg/L, respectively, exceeding the pure heated control at 140 °C (296 ± 6.67 μg/L). The total concentration of furans was enhanced to (20.7 × 10³) ± 8.17 μg/L by extra-added Gln. Different increasing effects were observed on the type and flavor intensity of formed pyrazines and furans from different extra-added amino acids.

Evaluation of the composition of konjac glucomannan on the color changes during the deacetylation reaction

As a newly superior konjac variety, the Amorphophallus bulbifer (A. bulbifer) has several unique advantages of high reproductive coefficient, short growth cycle, high disease resistance, high konjac glucomannan (KGM) content and climate adaption to hot or humid conditions. However, the gel formed by KGM from the A. bulbifer flour is easily browning during the alkali-induced process and the mechanism underlying them is still unclear. In order to explore the browning mechanisms, the changes of composition and color parameters of KGM were investigated during deacetylation in this research. The L*, h*, total phenols, total flavonoids, reducing sugars, and amino acids decreased along with the increase of deacetylation degree of KGM while a*, ΔЕ, and browning index increased. The results indicated that the oxidation or polymerization of polyphenols and flavones in alkaline circumstances, and the carbonyl ammonia reaction between reducing sugars and amino acids may be the main reasons for color changes of KGM flour during deacetylation. Hence, this study was expected to provide the theoretical basis for the inhibition of KGM gel browning and further broaden the application range of KGM in food and other industries.

Comparison of Color Development Kinetics of Tanning Reactions of Dihydroxyacetone with Free and Protected Basic Amino Acids

Sunless tanning has become incredibly prevalent due to the increasing fashionable demand and the awareness of photodamage risks. The brown pigments are induced by dihydroxyacetone (DHA) and amino groups in the stratum corneum (SC) of skin via the Maillard reaction. While most studies concerning sunless tanning reactions have focused on free amino acids (AAs), little information is available on the impact of the side chain of AAs or proteins on this important reaction in cosmetic chemistry. To explore the reactivity and color development kinetics of different types of amino groups, three basic free AAs (Arg, His, and Lys) and three Nα-protected AAs (Boc-Arg-OH, Boc-His-OH, and Boc-Lys-OH) were used to react with DHA using a simplified model system at different reaction times, pH, and temperatures. Full factorial experiments were employed to design and analyze the effects of these three factors. The browning intensity and color characteristics were quantitatively evaluated. The factorial experiments showed that temperature had the most significant influence on the browning intensity and played a dominant role in the interactions with the reaction time and pH. It was found, for the first time, that Arg and His reacted with DHA more rapidly than Boc-Arg-OH and Boc-His-OH, while Boc-Lys-OH developed a stronger color than Lys under the same conditions, suggesting that ε-NH₂ of a lysine residue in peptides or proteins of SC may play a crucial role in the color development of DHA tanning. This study not only clearly illustrates the capability of the side chain of AAs to produce colored compounds but also provides a deeper understanding of DHA tanning.

Effect of a Multifunctional Biosurfactant Extract Obtained from Corn Steep Liquor on Orange and Apple Juices

Biosurfactant extracts are multifunctional ingredients composed of natural polymers that can be used in the food industry as stabilizing and antimicrobial agents, although their inclusion in food matrices has been scarcely explored. In this work, a biosurfactant extract, with antimicrobial properties, obtained from a fermented stream of the corn wet-milling industry was introduced into an apple and orange juice matrix to evaluate the changes produced in the sugar consumption, pH, and biomass formation at different temperatures (4–36 °C) and storage time (1–7 days). It was observed that the addition of biosurfactant extract reduced the hydrolysis rate of polymeric sugars, decreasing the concentration of soluble sugars from 85.4 g/L to 49.0 g/L in apple juice after 7 days at 20 °C in the absence and presence of biosurfactant extract, respectively. In general, soluble sugars increased in juices for 5–6 days and after those sugars decreased at different rates depending on the temperature of storage. Differences in sugar solubilization and degradation were more significant in apple juice than in orange juice at 20 °C and 7 days of storage, achieving for orange juice values of 101 and 102 g/L in the absence and presence of biosurfactant extract, respectively. Biomass growth was almost unaffected by the biosurfactant extract concentration and the optimal conditions for biomass production were detected at intermediated temperatures after 6–7 days of storage for both apple and orange juices, obtaining maximum concentrations of 1.68 g/L and 1.54 g/L for apple juice and orange juice, respectively, in the absence of biosurfactant extract. The pH during storage was kept in the range of 3.35–3.48 for apple juice and of 3.40–3.77 for orange juice.

Efficient Production of 2,5-Diketo-D-gluconic Acid by Reducing Browning Levels During Gluconobacter oxydans ATCC 9937 Fermentation

D-Glucose directly generates 2-keto-L-gulonic acid (2-KLG, precursor of vitamin C) through the 2,5-diketo-D-gluconic acid (2,5-DKG) pathway. 2,5-DKG is the main rate-limiting factor of the reaction, and there are few relevant studies on it. In this study, a more accurate quantitative method of 2,5-DKG was developed and used to screen G. oxydans ATCC9937 as the chassis strain for the production of 2,5-DKG. Combining the metabolite profile analysis and knockout and overexpression of production strain, the non-enzymatic browning of 2,5-DKG was identified as the main factor leading to low yield of the target compound. By optimizing the fermentation process, the fermentation time was reduced to 48 h, and 2,5-DKG production peaked at 50.9 g/L, which was 139.02% higher than in the control group. Effectively eliminating browning and reducing the degradation of 2,5-DKG will help increase the conversion of 2,5-DKG to 2-KLG, and finally, establish a one-step D-glucose to 2-KLG fermentation pathway.

Applications of Innovative Non-Thermal Pulsed Electric Field Technology in Developing Safer and Healthier Fruit Juices

The deactivation of degrading and pectinolytic enzymes is crucial in the fruit juice industry. In commercial fruit juice production, a variety of approaches are applied to inactivate degradative enzymes. One of the most extensively utilized traditional procedures for improving the general acceptability of juice is thermal heat treatment. The utilization of a non-thermal pulsed electric field (PEF) as a promising technology for retaining the fresh-like qualities of juice by efficiently inactivating enzymes and bacteria will be discussed in this review. Induced structural alteration provides for energy savings, reduced raw material waste, and the development of new products. PEF alters the α-helix conformation and changes the active site of enzymes. Furthermore, PEF-treated juices restore enzymatic activity during storage due to either partial enzyme inactivation or the presence of PEF-resistant isozymes. The increase in activity sites caused by structural changes causes the enzymes to be hyperactivated. PEF pretreatments or their combination with other nonthermal techniques improve enzyme activation. For endogenous enzyme inactivation, a clean-label hurdle technology based on PEF and mild temperature could be utilized instead of harsh heat treatments. Furthermore, by substituting or combining conventional pasteurization with PEF technology for improved preservation of both fruit and vegetable juices, PEF technology has enormous economic potential. PEF treatment has advantages not only in terms of product quality but also in terms of manufacturing. Extending the shelf life simplifies production planning and broadens the product range significantly. Supermarkets can be served from the warehouse by increasing storage stability. As storage stability improves, set-up and cleaning durations decrease, and flexibility increases, with only minor product adjustments required throughout the manufacturing process.

Comparison of the Effects of High Pressure Processing, Pasteurization and High Temperature Short Time on the Physicochemical Attributes, Nutritional Quality, Aroma Profile and Sensory Characteristics of Passion Fruit Purée

The study investigated the effects of high-pressure processing (HPP) (600 MPa/5 min), pasteurization (PT) (85 °C/30 s), and high-temperature short time (HTST) (110 °C/8.6 s) on physicochemical parameters (sugar, acid, pH, TSS), sensory-related attributes (color, aroma compounds), antioxidants (phenolics, vitamin C, carotenoids, antioxidant capacity), and sensory attributes of yellow passion fruit purée (PFP). Compared to the PT and HTST, HPP obtained the PFP with better color, sugar, and organic acid profiles. Although PT was equally effective preservation of antioxidants and antioxidant capacity of PFP compared to HPP, high temperature inevitable resulted in the greater degradation of the aroma profile. The amounts of esters, alcohols, and hydrocarbon in PFP were significantly increased by 11.3%, 21.3%, and 30.0% after HPP, respectively. All samples were evaluated by a panel comprising 30 panelists according to standard QDA (quantitative descriptive analysis) procedure, and the result showed that HPP-treated PFP was rated the highest overall intensity score with 7.06 for its sensory attributes, followed by control (6.96), HTST (6.17), and PT (6.16). Thus, HPP is a suitable alternative technology for achieving the good sensory quality of PFP without compromising their nutritional properties.

Reaction pathways and factors influencing nonenzymatic browning in shelf-stable fruit juices during storage

The occurrence of nonenzymaticbrowning in fruit juices during storage is a major quality defect. It negatively affects consumer acceptance and consumption behavior and determines the shelf-life of these products. Although nonenzymatic browning of fruit juices has been the subject of research for a long time, the exact mechanism of the nonenzymatic browning reactions is not yet completely understood. This review paper aims to give an overview of the compounds and reactions playing a key role in nonenzymatic browning during the storage of fruit juices. The chemistry of the plausible reactions and their relative importance will be discussed. To better understand nonenzymatic browning, factors affecting these reactions will be reviewed and several strategies and methods to evaluate color changes and browning will be discussed. Nonenzymatic browning involves three main reactions: ascorbic acid degradation, acid-catalyzed sugar degradation, and Maillard-associated reactions. The most important NEB pathway depends on the matrix. Nonenzymatic browning is affected by many factors, such as the juice composition, the pH, the oxygen availability (packaging material), and the storage conditions. Nonenzymatic browning can thus be considered as a complex problem. To characterize color changes and browning and obtain insight into the browning mechanism of fruit juices, food scientists applied several approaches and strategies. These included the use of model systems with/without the addition of labeled compound and real systems as well as advanced analytical methods.

A prototype device of microliter volume voltammetric pH sensor based on carbazole-quinone redox-probe tethered MWCNT modified three-in-one screen-printed electrode

As an alternate for the conventional glass-based pH sensor which is associated with problems like fragile nature, alkaline error, and potential drift, the development of a new redox-sensitive pH probe-modified electrode that could show potential, current-drift and surface-fouling free voltammetric pH sensing is a demanding research interest, recently. Herein, we report a substituted carbazole-quinone (Car-HQ) based new redox-active pH-sensitive probe that contains benzyl and bromo-substituents, immobilized multiwalled carbon nanotube modified glassy carbon (GCE/MWCNT@Car-HQ) and screen-printed three-in-one (SPE/MWCNT@Car-HQ) electrodes for selective, surface-fouling free pH sensor application. This new system showed a well-defined surface-confined redox peak at an apparent standard electrode potential, Eo' = - 0.160 V versus Ag/AgCl with surface-excess value, Γ = 47 n mol cm-2 in pH 7 phosphate buffer solution. When tested with various electroactive chemicals and biochemicals such as cysteine, hydrazine, NADH, uric acid, and ascorbic acid, MWCNT@Car-HQ showed an unaltered redox-peak potential and current values without mediated oxidation/reduction behavior unlike the conventional hydroquinone, anthraquinone and other redox mediators based voltammetry sensors with serious electrocatalytic effects and in turn potential and current drifts. A strong π-π interaction, nitrogen-atom assisted surface orientation and C-C bond formation on the graphitic structure of MWCNT are the plausible reasons for stable and selective voltammetric pH sensing application of MWCNT@Car-HQ system. Using a programed/in-built three-in-one screen printed compatible potentiostat system, voltammetric pH sensing of 3 μL sample of urine, saliva, and orange juice samples with pH values comparable to that of milliliter volume-based pH-glass electrode measurements has been demonstrated.

Potential of 1H NMR fingerprinting and a model system approach to study non-enzymatic browning in shelf-stable orange juice during storage

For the first time, a model system approach was combined with ¹H NMR fingerprinting in studying non-enzymatic browning (NEB) of pasteurized shelf-stable orange juice during storage. Various NEB precursors were used individually or in combinations to formulate simple or complex model systems, respectively, in citric acid buffer. Based on orange juice composition, ascorbic acid, sugars (sucrose, glucose and fructose) and amino acids (proline, arginine, asparagine, aspartic acid, serine and glutamic acid) were selected as the precursors for the model systems. After pasteurization and during subsequent accelerated storage (42 °C, 16 weeks) the model systems displayed a three-phase browning development. The initial browning phase was mainly the result of ascorbic acid degradation especially in the presence of amino acids and sugars. In the later phases, the contribution of reactions of sugars and amino acids to browning became apparent. The application of ¹H NMR fingerprinting on a simple model system containing ascorbic acid revealed that its degradation pathway to intermediates such as xylonic acid, acetic acid and erythrulose was responsible for the major changes during storage. When this model system was complexed by inclusion of sugars and amino acids, the hydrolysis of sucrose to glucose and fructose was identified as the main reaction leading to differences in the samples throughout storage. These three sugars dominated the NMR spectra of the samples, overshadowing several important compounds for NEB such as ascorbic acid and its degradation products. Other more advanced NMR experiments such as two-dimensional NMR analyses should be applied in future research to identify unknown compounds from NEB reactions.