Application of Vacuum Frying as a Furan and Acrylamide Mitigation Technology in Potato Chips

Consumers like fried snacks, and taste, color, and texture are key aspects in their preference. However, during frying of foods some toxic compounds, such as furan and acrylamide, are produced. The objective of this work was to mitigate furan and acrylamide formation in potato chips, without affecting their main quality attributes, by using vacuum frying. To accomplish this purpose, potato slices were fried at atmospheric (P _abs 29.92 inHg) and vacuum conditions (P _abs 3.00 inHg), using equivalent thermal driving forces (T _{water boiling point} ? T _oil = 50, 60, or 70 °C). Furan and acrylamide concentration, oil content, and texture of both atmospheric and vacuum-fried samples were determined. Vacuum-fried potato chips showed reductions of about 81, 58, and 28% of furan, acrylamide, and oil content, respectively, when compared to their atmospheric counterparts. Additionally, the texture was not affected (p > 0.05) by changes in the pressure during frying. Results clearly showed that vacuum frying is an effective technology for furan and acrylamide mitigation in potato chips, since it reduces the content of both contaminants and preserves the quality attributes of fried snacks.     

Non-Thermal Pasteurization of Orange (<Emphasis Type="Italic">Citrus sinensis</Emphasis> (L.) Osbeck) Juices Using Continuous Pressure Change Technology (PCT): a Proof-of-Concept

Non-thermal pasteurization of orange juices using a continuous pressure change technology (PCT) device was investigated on pilot plant scale for the first time. PCT treatment was conducted by pressurizing orange juice and nitrogen at moderately high pressures (P?=?25 or 50 MPa) in a tubular continuous reactor. Abrupt decompression was achieved by a relief valve at the end of the tubular system. As compared to freshly squeezed juice, PCT treatment slightly reduced levels of carotenoids, vitamin C and hesperidin by 19, 5, and 14 %, respectively. Peroxidase was completely inactivated, whereas residual pectin methylesterase activities amounted to 26–27 %. Simultaneously, total aerobic plate counts were substantially reduced by at least 3.4 log₁₀ cfu/mL. The mean volume-weighed particle diameter d ₄₃ was drastically reduced from 652 μm in freshly squeezed juice to 6 and 31 μm at 25 and 50 MPa, respectively. Concomitantly, CIE-L*a*b* color values indicated a brighter and more intense yellow color of PCT-treated juices. While cloud separation in freshly squeezed juice was completed within 3 days, cloud stability in PCT-treated juices was retained for 5 days.     

Impact of Thermal and Pressure-Based Technologies on Carotenoid Retention and Quality Attributes in Tomato Juice

The aim of this study was to investigate the impact of thermal processing (TP) (90 °C, 90 s), high-pressure processing (HPP) (600 MPa, 46 °C, 5 min), and high-pressure homogenization (HPH) (246 MPa, 99 °C, <1 s) on product quality parameters, specifically carotenoid content, and physicochemical attributes of particle size, color, viscosity, total soluble solids, and pH in tomato juice. Unprocessed tomato juice was used as control. The four major species of carotenoids (lycopene, β-carotene, phytoene, and phytofluene) in tomato juice were analyzed by HPLC. The content of total lycopene, all-trans-lycopene, cis-lycopene isomers,  phytoene, and phytofluene, in TP-, HPP-, and HPH-treated tomato juice did not significantly differ from that in unprocessed (control) juice. Significant reduction in β-carotene content was observed after TP treatment but not after HPP and HPH treatments. HPH significantly reduced tomato juice particle volume mean diameter from ～330 μm in control, HPP-, and TP-treated tomato juices to ～17 μm. A concomitant increase in apparent viscosity was observed in HPH-treated juice versus control. HPH-treated juice had increased redness (a*) and yellowness (b*) than that in control and HPP-treated tomato juices. These results indicate that high-pressure-based technologies (HPP and HPH) can preserve carotenoids as well as improve physicochemical properties.     

Effect of Cold Atmospheric Plasma on Inactivation of <Emphasis Type="Italic">Escherichia coli</Emphasis> and Physicochemical Properties of Apple,Orange, Tomato Juices,and Sour Cherry Nectar

In this study, orange, tomato, apple juices, and sour cherry nectar were exposed to an atmospheric pressure plasma jet. Plasma treatments were carried out using air as a precursor under constant gas flow (3000 L/h) at 650 W for different treatment times (30, 60, 90, and 120 s). After plasma processing, reduction of Escherichia coli, Hunter’s color parameters (L*, a*, b*), total phenolic content, and pH values were evaluated. The inactivation effect of cold atmospheric plasma (CAP) was investigated on E. coli, and the highest significant reductions were achieved in apple juice (4.02 ± 0.03 log CFU/mL) followed by sour cherry (3.34 ± 0.09 log CFU/mL), while the values in orange (1.59 ± 0.17 log CFU/mL) and tomato juices (1.43 ± 0.22 log CFU/mL) were lower, which could be attributed to the food matrix. Color parameters, except for apple juice, did not show significant changes after processing. Compared to untreated juice, plasma treatment yielded higher phenolic content from 10 to 15%, while pH values did not change significantly and the temperature remained below 40 °C after all plasma treatments. This study showed that CAP treatment had positive influences on phenolic stability and color change in all samples regardless of food intrinsic factors, while it was more effective on bacterial inactivation in clear juices than turbid ones. Our results indicate that atmospheric plasma appears to be a promising technology for microbial inactivation without causing undesirable changes in food product.     

Effect of isomaltulose used for osmotic extraction of <Emphasis Type="Italic">Prunus mume</Emphasis> fruit juice substituting sucrose

This study evaluated the applicability of isomaltulose as a sucrose substitute in the osmotic extraction of Prunus mume fruit juice. Isomaltulose (20 mM) significantly reduced the uptake of a fluorescent tracer—2-[N-(7-nitrobenz-2-oxa-1,3-diaxol-4-yl) amino]-2-deoxyglucose. Juice extracted by isomaltulose had similar pH and titratable acidity values to those of the other sugars. Citric and malic acids were the main organic acids in the extracted juices. The radical-scavenging ability of the plum juice extracted by isomaltulose was significantly higher than in juices extracted by other sugars (p?<?0.05) and polyphenols content of the juice was also significantly higher than those of other sugars. The blood glucose level of P. mume juice extracted by fructose or isomaltulose was increased slowly compared to the juice extracted by sucrose. Therefore, the use of isomaltulose or an isomaltulose mixture in the manufacture of P. mume juice will help maintain health by reducing sugar intake.     

Discrimination of <Emphasis Type="Italic">Alicyclobacillus</Emphasis> Strains by Lipase and Esterase Fingerprints

Alicyclobacillus spp. have recently become a major issue in the fruit juice industry due to its implication in the spoilage of pasteurized juices/beverages. In this study, lipase and esterase fingerprints of 37 Alicyclobacillus strains and 14 Bacillus strains in apple juice were collected using a five-substrate cocktail including four C8-esters and one C4-diester. Characterization of each strain could be finished in a single assay followed by high-performance liquid chromatography (HPLC) analysis for product separation and quantification. The obtained lipase and esterase fingerprints were highly species-dependent. Differences between the relative peak areas of each product for different species were significant. Coupled to chemometric techniques including principal component analysis (PCA) and stepwise linear discriminant analysis (SLDA), the lipase and esterase profiles led to 100 % of correct species identification for Alicyclobacillus and Bacillus strains. This approach is promising, reliable, and with good repeatability and could be used as an alternative tool to discriminate Alicyclobacillus spp. in fruit juices.     

Fabricating a Novel Raman Spectroscopy-Based Aptasensor for Rapidly Sensing <Emphasis Type="Italic">Salmonella typhimurium</Emphasis>

A novel surface-enhanced Raman scattering (SERS) response emerging from aptamers, complementary DNA (cDNA), p-aminothiophenol (PATP), and Au nanorods (GNRs) for detection of foodborne pathogens sensitivity is proposed here. In the presence of Salmonella typhimurium (ST) and cDNA simultaneously, ST and cDNA would competitively combine with the S. typhimurium aptamer (STA), inducing a highly conformation changes of STA. Accordingly, STA no longer stabilizes the GNRs in salt solution, leading to the varying aggregation extent of GNRs. The varying GNR aggregation will give rise to the plasmonic coupling and display a strong SERS signal, which can be distinctly reflected by the attached PATP via a transition of signals typical from ST peaks to PATP peaks. Under optimal conditions, the SERS intensity was observed to increase linearly with ST concentration from 56 to 56 × 10⁷ cfu/mL (R ² = 0.971), with a LOD of 9 cfu/mL. Additionally, this aptasensor exhibits a high selectivity to other similar pathogens, and the ability of the bioassay to detect ST was also confirmed in adulterated milk samples.     

Analysis of Ascorbic Acid and Isoascorbic Acid in Orange and Guava Fruit Juices Distributed in Thailand by LC-IT-MS/MS

This work describes the determination of ascorbic acid (AA) and isoascorbic acid (IAA) in fruit juices by liquid chromatography coupled with ion trap tandem mass spectrometry (LC-IT-MS/MS), with a reversed phase column (C₁₈) and simple isocratic conditions of 0.1 % formic acid. The negative ion mode of electrospray ionization (ESI) and the MS/MS transition of m/z 175 were used for the quantitation of AA- and IAA-generated product ions with m/z 115. The method was validated in terms of linearity, limit of detection (LOD), limit of quantitation (LOQ), precision, and accuracy. Good linearity was achieved with 0.6 and 1.8 μg/mL for the LOD and LOQ, respectively. The intraday and intermediate precisions were approximately 4 and 7 %, respectively. Recovery percentages ranged from 88 to 108 %. All validation parameters were found to be within the acceptable range for both AA and IAA. Hence, the proposed method is suitable for simultaneously determining AA and IAA. Fourteen fruit juice samples were analyzed including fruit juices from supermarkets, local markets, and laboratory preparations. Ten fruit juice samples (100 %) from different brands in the supermarkets were investigated for AA and IAA content. AA could be detected in all the samples, ranging from 5.2?±?2 to 44.4?±?1.3 μg/mL, and the values of vitamin C in 4 guava samples were less than the values specified by the manufacturer. IAA was observed in 4 of 10 samples ranging from 3.4?±?0.9 to 78.3?±?3.9 μg/mL, and the highest value of IAA was approximately two fold higher than the highest value of AA. For freshly prepared fruit juices, AA was detected in both local market- and laboratory-prepared juices. The value ranged from 13.2?±?0.9 to 105.1?±?1.3 μg/mL. In addition, the AA stability after opening the package was evaluated. The results showed that after 4 days of storage in the refrigerator, approximately 30 and 15 % losses of AA were observed for the orange and guava juices, respectively. Fresh fruit juices were thus demonstrated to be good sources of AA, with the highest value observed for guava juice prepared in the laboratory.     

Evaluation of colour properties and chemical quality parameters of cactus juices

The chemical composition and visual appearance of cactus fruits from the genera Opuntia and Hylocereus were investigated. Colour properties were assessed in solutions with pH ranging from 1 to 8 and expressed as chroma, hue and colour shade. Between pH 3 and 7, all samples were stable as indicated by hue and chroma values. The colour shade of the red juice of Opuntia ficus-indica cv. 'Rossa' was in the range of red beet preparations hitherto most commonly used for colouring low-acid food commodities. Hylocereus was characterized by purplish hues, whereas the juice from O. ficus-indica cv. 'Gialla' displayed a yellow tonality. An improved spectrophotometric method for pigment quantification was proposed. Betacyanin contents were 525.3, 73.9 and 1.3 mg/l in juices from Hylocereus polyrhizus, Opuntia ficus-indica cv. 'Rossa' and O. ficus-indica cv. 'Gialla', whereas betaxanthins amounted to 48.3, 36.4 and 5.3 mg/l in O. ficus-indica cv. 'Gialla', O. ficus-indica cv. 'Rossa', and H. polyrhizus, respectively. Although the colourless fruits from O. ficus-indica cv. 'Bianca' and H. undatus could not be considered as a colour source, selected quality parameters were also investigated with respect to their nutritional value. To the best of our knowledge, this is the first report about the chemical quality parameters of H. polyrhizus and H. undatus.     

Effect of Solids Concentration on the Physicochemical and Flow Properties of Cactus Pear Juices of Two Varieties (<Emphasis Type="Italic">Opuntia ficus-indica</Emphasis> and <Emphasis Type="Italic">Opuntia streptacantha</Emphasis>)

Juices from two varieties of cactus pear, a green (Opuntia ficus-indica) and a red (Opuntia streptacantha), were obtained and concentrated by evaporation. Both fruit varieties and their juices at different concentrations were characterized. Green cactus pears had significantly higher amount of pulp than red cactus pears; the peel of O. ficus-indica represented only 38 versus 52 % of the fruit for the O. streptacantha. Both varieties had no significant differences on moisture, density, pH, and titratable acidity, in contrary to soluble solids. Juice was concentrated under vacuum conditions to reach a final concentration of 42, 53–55, and 58–60 °Brix, respectively, and stored under refrigeration (10 °C) during 4 weeks. Physicochemical properties of the pears and juices were determined as fresh items (time zero) and every week for the concentrate juices through storage; similarly, flow parameters were measured at 10 and 25 °C. Concentrate density (1160–1283 kg/m³) was mainly affected by final soluble solids, while pH and acidity were affected differently depending on the variety. Concentrated juices at 42 °Brix were considered with Newtonian behavior with a viscosity of 2–22 mPa s, while those at higher concentrations were of pseudoplastic nature (n < 1.0 and K > 69 mPa sⁿ). Power Law model fitted better the flow behavior than Herschel-Bulkley model of concentrates of both varieties. Temperature, solid concentration, and/or storage time affected the consistency coefficient (K) and flow index (n) depending on the cactus pear variety. Overall, those concentrated juices from O. streptacantha were more stable and exhibited lower apparent viscosity.     

Combined Use of Ultrasound and Vanillin to Improve Quality Parameters and Safety of Strawberry Juice Enriched with Prebiotic Fibers

In this work, a previously optimized preservation treatment (vanillin = 1.25 mg/mL; ultrasound = 7.5 min, 40 kHz, 180 W) was applied to strawberry juice enriched with inulin and oligofructose. The evolution of microbial, nutritional, and sensory parameters of treated juices was studied. It was confirmed that the inclusion of inulin and oligofructose had no negative implication regarding the quality of fresh juice. Furthermore, the prebiotic addition maintained sensory attributes of the product. The applied preservation treatment improved almost every quality attribute during storage, reducing microbial development, especially lactic acid bacteria and yeast and mold growth, which rapidly grew in untreated juices. Nutritional quality was also improved by the treatment as total polyphenol and total flavonoid content were increased and ascorbic acid content losses were reduced during storage, indicating higher antioxidant capacity. Overall, the evaluated sensory attributes of treated juices were deemed acceptable (>2.5). The addition of vanillin imparted pleasant flavor notes to the juice, compatible with the fruit product. Also, the performance of the treated juice was evaluated against postharvest contaminations with pathogens of interest in the food industry and of health concern (Escherichia coli O157:H7 and Listeria monocytogenes, evaluated through the surrogate Listeria innocua). The optimized treatment was able to reduce the counts of these microorganisms during storage reaching undetectable values after 7 days of storage. Thus, the combination of vanillin and ultrasound could be a feasible alternative to ensure safety and improve quality parameters of strawberry juice enriched with prebiotic fibers.     

Comparing the Impact of High-Pressure Processing and Thermal Processing on Quality of “Hayward” and “Jintao” Kiwifruit Purée: Untargeted Headspace Fingerprinting and Targeted Approaches

This study evaluated process-induced quality changes in kiwifruit purée of two commercial cultivars (green kiwifruit, “Hayward”, and gold kiwifruit, “Jintao”) treated by equivalent microbial safety-based processing: high-pressure processing (HPP; 600 MPa/3 min) and thermal processing (TP; P ^{85 °C} _{8.3 °C} = 5min). This comparative study was performed using both targeted, analyzing a priori selected quality attributes (color, sugars, organic acids, and vitamin C) and untargeted headspace-solid phase microextraction-gas chromatography-mass spectrometry approaches, combining multivariate data analysis techniques (partial least squares discriminant analysis and variable identification). HPP provided a better retention of color and vitamin C compared to TP. Sugar and organic acid were less affected by HPP and TP. Methyl and butyl esters were detected at higher amounts in both processed purée, compared to untreated purée. For processed samples, furanones, terpenes, and alcohols were detected at higher amounts after TP and aldehydes were detected at higher amount after HPP. Overall, the quality of HP-treated samples is clearly closer to that of fresh samples compared to thermally treated samples and HP treatment avoids the formation of typical temperature-induced compounds.     

Quality Changes in Mango Juice Treated by High-Intensity Pulsed Electric Fields Throughout the Storage

The effect of high-intensity pulsed electric fields (HIPEF) processes on Listeria innocua inhibition, physicochemical parameters and activity of oxidative enzymes of mango juice was evaluated to set the optimal HIPEF treatment time. Quality parameters, microbial population and bioactive compounds of HIPEF-treated (35 kV/cm, 1800 μs) and thermally treated (TT) (90 °C, 60 s) mango juices were studied and compared with those non-treated during 75 days of storage at 4 °C. HIPEF treatment for 800 μs ensured 5 log reductions of L. innocua. Polyphenoloxidase (PPO), lipoxygenase (LOX) and peroxidase (POD) residual activities were significantly reduced to 70, 53 and 44%, respectively, at treatment times of 1800 μs. Similar sensory properties compared with fresh mango juice were attained from product treated at 1800 μs. Moreover, fresh mango juice colour (L* = 38.79, h° = 106.57) was preserved after HIPEF treatment throughout storage. Moulds and yeasts and psychrophilic bacteria counts in HIPEF-treated (1800 μs) mango juice remained below 6 log cycles CFU/mL up to 2 months of refrigerated storage. The content of total phenolic compounds in those HIPEF-treated increased from 333 to 683 μg of GAE/mL from day 0 to the end of storage. Hence, the application of HIPEF may be a feasible treatment in order to ensure microbiological stability, high bioactive compound content and fresh-like characteristics of mango juice.     

Smart NMR Method of Measurement of Moisture Content of Vegetables During Microwave Vacuum Drying

Microwave drying is usually combined with vacuum environment in conjunction with hot air flow to draw the moisture rapidly. The moisture content of the vegetables undergoing drying is hard to measure online. This research designed a microwave vacuum drying (MVD)-low-field nuclear magnetic resonance (NMR) smart device and investigated the feasibility of NMR method for online measurement of state of moisture during MVD. The relation between the signal amplitude (A ₂) and the true moisture content (M ₁) of six kinds of vegetables (mushroom, carrot, potato, lotus, edamame, vegetable corn) was fitted to estimate if NMR can measure the M ₁ of vegetables directly. Results showed that A ₂ and M ₁ of different fresh vegetables had no single empirical mathematical model to fit. However, for each kind of these vegetables, the A ₂ and corresponding M ₁ in different MVD stages showed a significant linear relationship. The predicted moisture content (M ₂) of mushroom: M ₂ = 5.25351 × 10^?4 A ₂ ? 0.34042, R = 0.996; carrot: M ₂ = 5.78756 × 10^?4 A ₂ ? 0.14108, R = 0.998; potato: M ₂ = 3.10019 × 10^?4 A ₂ ? 0.10612, R = 0.991; lotus: M ₂ = 2.32415 × 10^?4 A ₂ ? 0.01573, R = 0.998; edamame: M ₂ = 3.13310 × 10^?4 A ₂ ? 0.4198, R = 0.996; vegetable corn: M ₂ = 1.69461 × 10^?4 A ₂ ? 0.09063, R = 0.995. The linear models between M ₂ and A ₂ were able to estimate the end point (M ₁ < 8%) of MVD with a high accuracy (P > 0.950).     

Chlorophyll Fluorescence Imaging for Monitoring the Effects of Minimal Processing and Warm Water Treatments on Physiological Properties and Quality Attributes of Fresh-Cut Salads

In this study, chlorophyll fluorescence imaging (CFI) was used to monitor plant stress induced by cutting of mini romaine lettuce (Lactuca sativa L. var. longifolia) and by cutting and washing of endive (Cichorium endivia L.) during storage. Regarding the more detailed study of endive fresh-cut salads, we additionally monitored respiratory activity, phenylalanine ammonia lyase (PAL) activity, contents of plant pigments, and cut edge browning. Determination of maximum quantum efficiency F _v/F _m was feasible through sealed consumer-sized film bags, thus, enabling the non-invasive monitoring of both fresh-cut salad types in the corresponding modified atmosphere during storage. Cutting of romaine lettuce provoked a partially reversible drop of F _v/F _m during the first 24 h. Subsequently, F _v/F _m of cut romaine strongly decreased with elapsing shelf life, whereas intact leaves exhibited only a slight decline. Regarding minimally processed endive, warm water washing progressively reduced F _v/F _m with increasing heat exposure, while respiratory activities and the content of accessory pigments remained unaffected. The heat-dependent decrease of F _v/F _m was correlated to the inhibition of the PAL activity. Mildly warm washing (40 °C, 120 s; 45 °C, 60 s) reduced PAL activities, while F_v/F_m remained widely unaffected and visual quality was only partially improved. However, warm water washing at elevated temperatures (45 °C, 120 s; 50 °C, 30–60 s) enabled maximum visual quality retention, accompanied by a significant decrease of F _v/F _m. CFI may represent a useful tool to monitor the stress conditions due to cutting and warm water treatments, hence, allowing the systematic improvement of fresh-cut produce.     

Effect of Addition of Native Agave Fructans on Spray-Dried Chayote (<Emphasis Type="Italic">Sechium edule</Emphasis>) and Pineapple (<Emphasis Type="Italic">Ananas comosus</Emphasis>) Juices: Rheology,Microstructure, and Water Sorption

The effect of the combination of maltodextrin DE 10 (MD) and native agave fructans (FR) in concentrations of 0, 2, and 4% (w/v) on the rheological properties, microstructure, and water sorption of spray-dried chayote and pineapple powders was evaluated. A 10% (w/v) maltodextrin treatment was used as a control to compare treatments added with fructans. The scanning electron micrographs revealed spherical particles in a range from 16 to 105 μm with shrinkage, whereby greater caking and agglomeration occurred among particles in treatments with native agave fructans. The flow behavior of all juices can be described by the Bingham model with low plastic viscosities (0.0026 to 0.0030 Pa s^?1); the isotherms of the powders show a sigmoid shape pointing to the easy union of the fructans with water molecules. These types of isotherms are common for non-porous foods, and are indicative of physical adsorption in multi-layers where the adsorbate conserves its identity.     

Development and characterization of reconstituted hydrogel from <Emphasis Type="Italic">Aloe vera</Emphasis> (<Emphasis Type="Italic">Aloe barbadensis</Emphasis> Miller) powder

Structural and rheological characterization of reconstituted hydrogels developed from A. vera non-fibrous alcohol insoluble residue (NFAIR) powder using different methods [viz., shaking (S), heating-shaking (HS), and heating (H)] and concentrations (viz., 0.2–1.6 %, w/v) was carried out. Functional group distribution by FTIR spectroscopy and Congo red (CR) method revealed the presence of acetylated acemannan in A. vera powder. Dynamic oscillation studies of A. vera (NFAIR) fluids at all concentrations of 0.2–1.6 %, w/v, showed gel strength in the order of H > HS > S method. However, in H method, increase in concentration from 0.2 to 1.6 %, w/v showed the conformational transition from semi-diluted solution to weak gel nature. Rheological models described the effect of heating temperatures (HT); 30–90 °C, and times (Ht); 15–60 min on viscoelastic behavior in reconstituted A. vera fluids. The reconstituted A. vera hydrogel prepared with a concentration of 1.6 %, w/v using 50 °C (HT) and 30 min (Ht) condition showed a good agreement with the Power law (storage modulus, G′) and Weak gel model (complex modulus, G*) fitted data (R² > 0.94) resulting higher viscoelastic moduli intercepts; G′₀ (71.5 Pa s ^n′), G″₀ (33.5 Pa s ^n″), lower slopes; n′ (0.22), n″ (0.06), higher network strength (A _F , 121.3 Pa s^1/z ) and number of network (z, 5.3) values. The obtained results suggested that heating at 50 °C/30 min can develop aqueous weak gel networks of A. vera with enhanced gel strength which may be utilized as a novel gelling agent for wide variety of targeted applications in food and pharmaceutical sectors.     

Effects of organic acid pretreatment on microstructure,functional and thermal properties of unripe banana flour

Starch availability has been implicated in unripe matured banana (Musa species), which when processed yields flour suitable for application in low gluten and composite wheat formulations. Unripe Musa species: Williams, Luvhele, Mabonde and Muomva-red obtained from fruit bunch were pretreated with ascorbic, citric and lactic acids, processed into 50 g of flour and characterised for their functional and thermal properties. Scanning electron microscope of unripe banana flour (UBF) showed varying micrographs of flour, with polygonal for Luvhele, oval for Mabonde, elongated for Muomva-red and between polygonal and spherical for Williams. The bulk density of UBF samples was within the range of 0.66–0.84 g/mL for all organic acid pretreatment while citric acid pretreated UBF had the least browning index. Significant difference (p < 0.05) was recorded in swelling power with no significant difference in water solubility index except for Mabonde UBF. Thermal properties showed single endothermic transition for all UBF samples at various pretreatment concentration. The onset temperature (To) of UBF ranges from 49.82 to 65.59 °C, peak temperature (Tp) from 60.11 to 76.71 °C, conclusion temperature (Tc) from 70.36 to 94.16 °C and enthalpy of gelatinization (ΔH) from 2.61 to 32.24 J/g. Short amylopectin chains present in starch of UBF was attributed to low To, Tp, Tc and ΔH values recorded for Mabonde cultivar, while the contribution of heat-moisture treatment rather than organic acid pretreatment of UBF samples was attributed to different gelatinization and transition temperatures recorded for all cultivars examined.     

Steaming time effects on the moisture migration and structural properties of Chinese Northern-style steamed bread

The aim of this study was to investigate the steaming time effects on proton transverse relaxation behavior with low field 1H nuclear magnetic resonance and structural properties of Chinese Northern-style steamed bread (CNSB). Three proton populations could be distinguished at the first 4 min: T_2b (0.1–1 ms) corresponded to rigid and exchangeable protons; T₂₂ (9–21 ms) was associated with the water protons in small and large meshes of the dough microstructure; T₂₃ (69–300 ms) was assigned to the water protons on the surface of samples. The starch gelatinization began and the water turned into the integral part of the biopolymer at 6 min, forming T₂₁ (1–3 ms) fraction. The gelatinization effect was strengthened up to 8 min and supplied a more mobile microenvironment, resulting in the increase of T₂₁, A₂₁ and M₂₁. However, the gelatinization process ended at 8 min, bringing about the stabilization of T₂₁, A₂₁ and M₂₁ until 25 min. T₂₂ fraction accounted for the largest proportion during all the steaming process. All variation trends on structural properties of CNSB and T₂ relaxation parameters including T_i, A_i (relative intensity of T_i), and M_i (population abundance of T_i) indicated that 6 and 8 min were the two transitions. The gluten matrix began to be disrupted at 6 min and was quite damaged up to 8 min by scanning electron microscopy. The peaks at 15°, 18°, 20°, and 23° in X-ray diffraction patterns appeared in the first 6 min but were lost up to 8, 10, and 25 min.     

Effect of Thermosonic Pretreatment and Microwave Vacuum Drying on the Water State and Glass Transition Temperature in <Emphasis Type="Italic">Agaricus bisporus</Emphasis> Slices

This study aimed to understand the micromechanism of thermosonic pretreatment and microwave vacuum drying on Agaricus bisporus. The water state and glass transition temperature (T _g ) of fresh and thermosonically treated Agaricus bisporus slices during microwave vacuum drying were studied using differential scanning calorimetry (DSC), low-field nuclear magnetic resonance (LF-NMR), and magnetic resonance imaging (MRI). Results showed that four population groups were contained in the initial distribution of transverse relaxation time (T ₂) data of fresh A. bisporus slices: T ₂₁ (0.38–7.05 ms), T ₂₂ (9.33–32.75 ms), T ₂₃₁ (37.65–265.61 ms), and T ₂₃₂ (305.39–811.13 ms). Thermosonic pretreatment significantly decreased the initial free water content of A. bisporus sample but was accompanied by a sharp increase in its immobilized water. “Semi-bound water transfer” appeared during microwave vacuum drying (MVD) at moisture contents (X _w ) of 0.70 and 0.60 g/g (wet basis (w.b.)) for untreated and thermosonically treated samples, respectively. MVD caused dramatic changes in the water state and enhanced the T _g by decreasing the content and mobility of immobilized water in A. bisporus tissues. The mobility of semi-bound water for thermosonically and MVD-treated samples was higher than for MVD-untreated samples, resulting in T _g values decreasing by approximately 2–11.5 °C, but the uniformity of water distribution in thermosonic-treated and MVD-treated samples was better at X _w  ≤ 0.52 g/g (w.b.).