Microbial Inactivation Kinetics in Soymilk during Continuous Flow High-Pressure Throttling

ABSTRACT:  The thermal resistance of  Clostridium sporogenes  PA 3679 ATCC 7955 was determined in soymilk (pH 7) and 0.1% peptone water (pH 7) by the capillary tube method. In the continuous flow high-pressure throttling, the temperature of soymilk increased due to instantaneous pressure release and the additional heat was supplied by a heat exchanger to achieve the set temperature. The soymilk was immediately cooled after a short preset hold time to below 40 °C. A significant increase in the heat resistance was observed in  C. sporogenes  spores when heated in soymilk in comparison to 0.1% peptone water. The  D ₁₂₁-value for spores in soymilk was approximately 3-folds higher than peptone water. The  z- value was also much higher in soymilk as compared to that in 0.1% peptone water. Continuous flow high-pressure throttling (HPT) from 207 or 276 MPa to atmospheric pressure reduced the microbial populations in inoculated soymilk up to 6 log cycles when the holding times were 10.4, 15.6, and 20.8 s and the process temperatures were 85, 121, 133, and 145 °C, respectively. The sporicidal effect increased as the operating pressure, time, and temperature were increased. More injured spores were found at 207 MPa than at 276 MPa, indicating that lower pressure caused cell injury whereas high pressure caused cell death.     

Efficacy of Pressure-Assisted Thermal Processing, in Combination with Organic Acids, against Bacillus amyloliquefaciens Spores Suspended in Deionized Water and Carrot Puree

ABSTRACT:  Effect of organic acids (acetic, citric, and lactic; 100 mM, pH 5) on spore inactivation by pressure-assisted thermal processing (PATP; 700 MPa and 105 °C), high pressure processing (HPP; 700 MPa, 35 °C), and thermal processing (TP; 105 °C, 0.1 MPa) was investigated.  Bacillus amyloliquefaciens  spores were inoculated into sterile organic acid solutions to obtain a final concentration of approximately 1.3 × 10⁸ CFU/mL.  B. amyloliquefaciens  spores were inactivated to undetectable levels with or without organic acids after 3 min PATP holding time. At a shorter PATP treatment time (approximately 2 min), the inactivation was greater when spores were suspended in citric and acetic acids than in lactic acid or deionized water. Presence of organic acids during PATP resulted in 33% to 80% germination in the population of spores that survived the treatment. In contrast to PATP, neither HPP nor TP, for up to 5 min holding time with or without addition of organic acids, was sporicidal. In a separate set of experiments, carrot puree was tested, as a low-acid food matrix, to study spore recovery during extended storage following PATP. Results showed that organic acids were effective in inhibiting spore recovery in treated carrot puree during extended storage (up to 28 d) at 32 °C. In conclusion, addition of some organic acids provided significant lethality enhancement ( P  < 0.05) during PATP treatments and suppressed spore recovery in the treated carrot puree.     

Alleviation effect of heat-treated and in vitro gastrointestinal digested soymilks on AAPH-induced oxidative stress in human erythrocytes: Digested soymilks alleviate oxidative stress

To investigate the potential protective effect of raw and heat-treated soymilks after gastrointestinal digestion against chemical oxidative stress induced by 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) on human erythrocytes, soymilk was subjected to heat treatment and in vitro gastrointestinal digestion. The inhibition rate of hemolysis, generation of reactive oxygen species (ROS), concentration of malondialdehyde (MDA), reduced glutathione (GSH) and oxidized glutathione (GSSH) and the enzyme activity of total superoxide dismutase (SOD) and cellular glutathione peroxidase (GPx) were evaluated as the biomarkers of oxidative status. Hemolysis of erythrocytes induced by AAPH was significantly inhibited by pretreatment with the digested raw soymilk (DRS) and digested heat-treated soymilk (DHS). Moreover, heat treatment prior to gastrointestinal digestion improved the inhibition effect of soymilk on erythrocytes hemolysis. The soymilk treated at 95 °C showed the highest inhibition rate, followed by 121 °C and 143 °C, revealed that the increase of temperature caused the decrease of hemolysis inhibition rate of DHS. Preincubation with the digested soymilks reduced the accumulation of MDA in erythrocytes, indicating the inhibition effect of the digested soymilks on lipid peroxidation. Results revealed that DRS and DHS alleviated the hemolysis of erythrocytes and lipid peroxidation resulted from oxidative stress by suppressing the accumulation of ROS, reducing the increase of SOD activity and decrease of non-enzymatic antioxidant GSH and enzymatic antioxidant GPx activity. Compared with raw soymilk, heat treatment improved the protective effect of the digested soymilk on erythrocytes against oxidative stress via enhancing the free radicals scavenging activity instead of improving the inhibition effect on the generation of free radicals.     

Feasibility of using dialysis for determining calcium ion concentration and pH in calcium-fortified soymilk at high temperature

Abstract: Dialysis was performed to examine some of the properties of the soluble phase of calcium (Ca) fortified soymilk at high temperatures. Dialysates were obtained while heating soymilk at temperatures of 80 and 100 °C for 1 h and 121 °C for 15 min. It was found that the pH, total Ca, and ionic Ca of dialysates obtained at high temperature were all lower than in their corresponding nonheated Ca‐fortified soymilk. Increasing temperature from 80 to 100 °C hardly affected Ca ion concentration ([Ca²⁺]) of dialysate obtained from Ca chloride‐fortified soymilk, but it increased [Ca²⁺] in dialysates of Ca gluconate‐fortified soymilk and Ca lactate‐fortified soymilk fortified with 5 to 6 mM Ca. Dialysates obtained at 100 °C had lower pH than dialysate prepared at 80 °C. Higher Ca additions to soymilk caused a significant (P≤ 0.05) reduction in pH and an increase in [Ca²⁺] of these dialysates. When soymilk was dialyzed at 121 °C, pH, total Ca, and ionic Ca were further reduced. Freezing point depression (FPD) of dialysates increased as temperature increased but were lower than corresponding soymilk samples. This approach provides a means of estimating pH and ionic Ca in soymilks at high temperatures, in order to better understand their combined role on soymilk coagulation.     

Effect of Pasteurization, High-Pressure Processing, and Retorting on the Barrier Properties of Nylon 6, Nylon 6/Ethylene Vinyl Alcohol, and Nylon 6/Nanocomposites Films

ABSTRACT:  This study determined the impact of pasteurization, high-pressure processing (HPP), and retorting on the barrier properties of nylon 6 (N6), nylon 6/ethylene vinyl alcohol (N6/EVOH), and nylon 6/nanocomposite (N6/nano) materials. The pasteurized and high-pressure treated films were coextruded with low-density polyethylene (PE) as the heat-sealing layer. The retorted films were coextruded with polypropylene (PP). Oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) of the samples were measured after pasteurization (75 °C for 30 min), HPP (800 MPa for 10 min at 70 °C), and retorting (121 °C for 30 min) treatments. These were compared with the thermal characteristics and morphologies of the samples using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Results showed that OTR of N6 and N6/Nano increased after HPP (16.9% and 39.7%), pasteurization (13.3% and 75.9%), and retorting (63.3% and 112.6%), respectively. For N6/EVOH, a decrease in OTR after HPP (53.9%) and pasteurization (44.5%) was observed. The HPP treatment increased the WVTR of N6 (21.0%), N6/EVOH (48.9%), and N6/Nano (21.2%). The WVTR of N6, N6/EVOH, and N6/Nano increased by 96.7%, 43.8%, and 40.7%, respectively, after pasteurization. The DSC analyses showed that the enthalpy and percent crystallinity increased (2.3% to 6.5%) in the N6/Nano when compared with the N6 material after each treatment. Retorting caused a decrease (3.5%) in the percent crystallinity of the polypropylene material. HPP did not cause major morphological changes to the samples. Results of the barrier studies were influenced by the crystallinity changes in the materials as seen in the XRD diffractograms.     

Conversion of isoflavone glucosides to aglycones in soymilk by fermentation with lactic acid bacteria

ABSTRACT:  Four lactic acid bacteria (LAB), Lactobacillus paraplantarum KM, Enterococcus durans KH, Streptococcus salivarius HM and Weissella confusa JY, were isolated from humans and tested for their capabilities of converting isoflavone glucosides to aglycones in soymilk. Changes in growth, pH, and titratable acidity (TA) were investigated during fermentation at 37 °C for 12 h. After 6 to 9 h of fermentation, each population of 4 LAB reached 10⁸ to 10⁹ CFU/mL. The initial pH of 6.3 ± 0.1 decreased while the TA of 0.13%± 0.01% increased as fermentation proceeded, resulting in the final range between 4.1 ± 0.2 and 4.6 ± 0.1 for pH and between 0.51%± 0.02% and 0.67%± 0.06% for TA after the 12 h of fermentation. The glucoside concentrations were significantly decreased in soymilks fermented with either L. paraplantarum KM, S. salivarius HM, or W. confusa JY with fermentation time ( P < 0.05). L. paraplantarum KM was the best in percent conversion of glucosides to corresponding aglycones, resulting in 100%, 90%, and 61% hydrolysis of genistin, daidzin, and glycitin, respectively, in 6 h. Consequently, the aglycone concentrations in soymilk fermented with L. paraplantarum KM were 6 and 7-fold higher than the initial levels of daidzein and genistein, respectively, after 6 h of fermentation. Changes in the daidzin and genistin levels were not significant in soymilk fermented with E. durans KH. The rates of hydrolysis of glucosides varied depending on the species of LAB. Especially, L. paraplantarum KM seems to be a promising starter for bioactive-fermented soymilk based on its growth, acid production, and isoflavone conversion within a short time.     

Production of Shelf-Stable Ranch Dressing Using High-Pressure Processing

ABSTRACT:  High-pressure processing (HPP) can reduce or eliminate microorganisms of concern in food without deteriorating product quality; however, quality benefits must justify the substantial capital investment for the utilization of this technology. HPP is particularly a beneficial preservation technology for products damaged by thermal treatments or when product quality could be improved by reformulation to raise pH or eliminate chemical preservatives. The primary objectives of this study were to determine the efficacy of HPP to protect premium ranch dressing (pH 4.4) from microbial spoilage and to assess changes in physical, chemical, and sensory attributes throughout the product's shelf life. In inoculated-packages studies, the efficacy of HPP was measured against ranch dressing spoilage organisms: Pediococcus acidilactici, Lactobacillus brevis, and Torulaspora delbrueckii . HPP treatment (600 MPa, 3 min) decreased population of P. acidilactici , the most pressure-resistant spoilage organism tested, by ≥ 6.4 log CFU/g. During a shelf-life study of edible product, treating ranch dressing at 600 MPa for 5 min effectively prevented microbial spoilage throughout the storage period (26 wk at 4 and 26 °C). The pH and emulsion stability of ranch dressing were not adversely influenced by HPP. Extended storage of HPP product for 16 to 26 wk at 26 °C resulted in a decrease in consumer acceptance and significant changes in color and organic acid profile (specifically, increased pyroglutamic acid). These changes were consistent with those expected during extended storage of commercially available products. HPP may be used to produce premium ranch dressing, with defined shelf-life and storage conditions, without significantly changing product attributes.     

Comparison of ultra high pressure homogenization and conventional thermal treatments on the microbiological,physical and chemical quality of soymilk

The effect of ultra high pressure homogenization (UHPH) at 200 and 300 MPa in combination with different inlet temperatures (55, 65 and 75 °C) on soymilk was studied. UHPH-treated soymilk was compared with the base product (untreated), with pasteurized (95 °C for 30 s) and with ultra high temperature (UHT; 142 °C for 6 s) treated soymilks. Microbiological (total aerobic meshophilic bacteria, aerobic spores, and Bacillus cereus), physical (dispersion stability and particle size distribution) and chemical (lipoxygenase activity, hydroperoxide index and trypsin inhibitor activity) parameters of special relevance in soymilk were studied. Microbiological results showed that pressure and inlet temperature combination had a significant impact on the lethal effect of UHPH treatment. While most of UHPH treatments applied produced high quality of soymilks better than that pasteurized, the combination of 300 MPa and 75 °C produced a commercially sterile soymilk. UHPH treatments caused a significant decrease in particle size resulting in a high physical stability of samples compared with conventional heat treatments. UHPH treatment produced lower values of hydroperoxide index than heat treated soymilks although trypsin inhibitor activity was lower in UHT-treated products.     

Stabilized soymilk for ambient tropical storage: a preliminary report

The shelf-stability of soymilks prepared from sterilized (121°C for 15min) water-soluble extracts of sprouted-blanched, sprouted-unblanched, and blanched whole soybeans (control) was evaluated; samples were compared for coagulation, pH, and loss of starch. The extract from sprouted-blanched soybeans remained uncoagulated for 6 weeks in ambient tropical storage, showed the greatest loss of starch and had the least total solids content (10%). The sprouted-unblanched soybeans produced an extract which coagulated instantly after sterilization at a pH of 5.6, the lowest pH value for treatment and control samples. The control contained the highest total solids (25%), showed least loss of starch and coagulated after 2 days in ambient tropical storage.     

Effect of High-Pressure Food Processing on the Physical Properties of Synthetic and Biopolymer Films

ABSTRACT:  The effect of high-pressure processing on 2 plastic food packaging films, a biopolymer (PLASiOx/PLA) and a synthetic polymer (PET-AlOx), was studied. Samples in direct contact with olive oil, as a fatty food simulant, and distilled water, as an aqueous simulant, were subjected to a pressure of 500MPa for 15 min at 50 °C. The mechanical, thermal, and gas barrier properties of both films were evaluated after the high-pressure processing (HPP) and compared to control samples that have not undergone this treatment. Significant changes in all properties were observed in both films after the HPP treatment and in contact with the food simulants. In both films an induced crystallization was noticed. In the PLASiOx/PLA film the changes were larger when in contact with water that probably acted as a plasticizer. In the PET-AlOx film the changes in properties were attributed to the formation of pinholes and cracks during the HPP treatment. In this film, most of the properties changed more in the presence of oil as the food simulant.     

PHYSICOCHEMICAL AND SENSORY CHARACTERISTICS OF FLAVORED SOYMILK DURING REFRIGERATION STORAGE1

The goal of this study was to investigate changes in physicochemical, microbiological, and sensory properties of flavored soymilk under refrigeration storage. The soymilk contained 85.7% moisture, 10.5% carbohydrates+ash, 2.2%protein, and 1.6% fat. Sensory analysis showed that chocolate and almond flavorings improved the aroma ofsoymilks (P < 0.05). Addition of gum partially masked the beany flavor and off‐flavor. All the soymilks had less than 10 CFU/mL of total aerobic, coliform, and E. coli counts. After one month's storage, TBARS decreased by about 20% (P < 0.05). All soymilk samples exhibited a pseudoplastic flow, and addition of 0.05% iota‐carrageenan increased their viscosity and shear stress (P < 0.05). Overall, flavored soymilks had improved desirable attributes and reduced undesirable characteristics over plain soymilk, and all were stable for one month at refrigeration condition.     

The properties and the related protein behaviors of oil bodies in soymilk preparation

Oil bodies (OBs), one of the major components of soymilk, are very important for the properties of soymilk and its related products. In this study, the properties and the related protein behaviors of OBs in the soymilk preparation were systematically examined. Raw soymilk OBs could keep their natural integrities after grinding, and they were bound by many soybean proteins (mainly β-conglycinin, glycinin, and Gly m Bd 30K) that could be removed by pH 11.0 washing. Heated soymilk OBs, including heat-induced coalesced OBs (>1 μm) and modified OBs (around 400 nm), were strongly bound by β-conglycinin and glycinin that even could not be removed by pH 11.0 washing. The oleosins (24 kDa, P29530 and P29531; 18 kDa, C3VHQ8) of raw soymilk OBs were hydrolyzed to 16 kDa polypeptides (on SDS–PAGE gel) when exposed to room temperature, while immediately heating, the raw soymilk could prevent the oleosin hydrolysis. Then, the isolated raw and heated soymilk OBs revealed different dispersion stabilities as a function of pH. At last, tofu curds were made from two reconstituted soymilks containing non-lipid soymilk and raw or heated soymilk OBs (pH 11.0 isolation), and one trend was found that tofu curds containing heated soymilk OBs had lower breaking stress and Young’s modulus than those containing raw soymilk OBs. It is considered that this study is meaningful for designing new strategies to improve the qualities of soymilk and its related products.     

CHANGES IN SOYMILK QUALITY AS A FUNCTION OF COMPOSITION AND STORAGE

ABSTRACT

Three soymilk products formulated with different concentrations of fat, sugar and starch were evaluated for changes in their physical properties and volatiles profile over time (3 months) under different temperatures (4, 22 and 38C) of storage. Samples were tested for pH, color, viscosity and volatile flavor changes. The pH and color of the soymilks decreased significantly during the first month of storage and then remained stable over time. Color and viscosity of the soymilk products were affected by both the soymilk composition and storage treatment. The high‐fat soymilk sample (product C) had the whitest color (lower ΔE) and the lowest viscosity. Storage at 38C negatively affected the color. The viscosities of the soymilk products stored at 4C were the lowest among the treatments. The major volatiles identified in all soymilk products were hexanal, heptanal, octanal, nonanal, hexanol, 1‐octen‐3‐ol, benzaldehyde, 2‐pentyl furan and 2‐ethyl furan. The intensities of the volatile compounds in the soymilk products increased during the first weeks of storage, particularly when stored at 38C. The intensities, however, decreased gradually over time. Among the three formulated soymilk products, the sweetened sample (product B) gave the lowest flavor intensities under all three temperatures of storage. Overall, storage at 4C and addition of sugar preserve best the soymilk quality.

PRACTICAL APPLICATIONS

Soy products are well appreciated for their nutritional and potential health benefits. Soy beverage consumption is increasing among North American consumers because of improvements in soy beverage quality and processing technologies. There is, however, a demand for new value‐added soy‐based drinks with improved “functional” (health‐benefiting) properties. Soy beverage could be an excellent carrier for “functional” or “nutritive” ingredients such as minerals, vitamins and omega 3 oils; however, addition of such ingredients may affect the stability of the product and requires the development appropriate of technologies for their incorporation. Results from this project provide new knowledge on the storage stability and quality of three different soy product formulations. The information could be useful in the establishment of optimal conditions for processing of functional soy beverages, for use by the food industry.

     

Effect of Continuous Flow High-Pressure Throttling on Rheological and Ultrastructural Properties of Soymilk

ABSTRACT:  Soymilk processing uses a filtration or centrifugation step to remove coarse solids in the comminuted soy. The objective was to utilize the whole beans and determine the effect of continuous flow high pressure throttling (CFHPT) process in reducing particle size and narrowing down the particle size distribution. The rheological and ultrastructural properties of such soymilk were also determined. Whole dehulled soybeans and deionized water were ground in a food processor before comminution in a Megatron (process M) or a Fitzmill (process F) or a Stonemill (process S). The comminuted slurry was homogenized at pressures of 69, 103, 138, 207, and 276 MPa using a CFHPT system, heated to 80 °C in a tubular heat exchanger prior to depressurization, and held at elevated temperatures of 97, 106, 114, 131, and 148 °C, respectively, for each applied pressure after throttling. To avoid flashing, back pressure was applied after the holding tube and soymilk was cooled immediately. Process M produced soymilk with smallest particle size and the highest apparent viscosity. All soymilk samples showed non-Newtonian pseudoplastic flow behavior. Ultrastructural images showed a clear protein network with very small fat globules entrapped in the protein matrix. Particles were uniformly distributed when the highest pressure treatment was applied for process M, which was considered as the best process.     

萌发大豆制备益生菌发酵豆乳流变特性的研究

以萌发大豆作为主要原料,经瑞士乳杆菌(Lactobacillus helveticus B02)、保加利亚乳杆菌(Lactobacillus bulgaricus AS1.1482)和嗜热链球菌(Streptococcus thermophilus IFFI 6038)组合发酵制成发酵豆乳,研究益生菌发酵豆乳的发酵特性及流变特性。结果表明,大豆经萌发后,游离氨基酸总量增加了近2倍;与未萌发大豆制成的发酵豆乳相比,萌发大豆发酵豆乳中乳酸菌菌落总数显著增加,产生更多的游离H离子及有机酸,且其剪切稀化作用减弱,表观黏度显著下降,更为接近发酵纯牛乳的流变特性。大豆萌发后制成发酵豆乳,可促进乳酸菌的生长及产酸,有助于改善发酵豆乳的流变特性。     

Sterilization and aseptic packaging of soymilk treated by ultra high pressure homogenization

Ultra high pressure homogenization (UHPH) was applied on soymilk to produce an aseptically packaged beverage. UHPH-treated soymilk (300 MPa, 80 °C inlet temperature and 144 °C/0.7 s at the homogenization valve) was compared with samples treated by ultra high temperature (UHT) at 142 °C for 6 s. After treatment, soymilk samples were aseptically packaged in coated paperboard cartons of 200 mL Tetra Brik containers. Tetra Brik containers were stored for 6 months at room temperature and analyzed at different days. Microbiological (total mesophilic aerobic bacteria, aerobic spores, Bacillus cereus, and enterobacteria counts), physical (dispersion stability and particle size distribution), chemical (hydroperoxide index and volatile profile evolution) and sensory analyses were performed on soymilks. Both UHPH and UHT soymilks did not present microbiological growth during storage. UHPH soymilk presented high colloidal stability and relevant decrease in hydroperoxide index during storage. On the other hand, almost all of the compounds associated to off-flavors were detected in the volatile profile of soymilk. Sensory results indicated that UHPH treatment did not produce changes in soymilk which could affect the panel perception for different UHT and UHPH soymilks and for selecting their preference.Industrial relevanceSoymilk constitutes one of the food industry sectors with the highest worldwide growth and its consumption has experienced a noticeable increase in the last years. The growing consumer demand for safe products, environmentally friendly processes and high quality nutritional foods has challenged the food industry to adapt the technological processes. This tendency impacts directly on traditional technologies, like heat treatments. In this sense, UHPH technology has been applied as an alternative to those thermal treatments. This research paper presents a comparative study between soymilk treated by UHPH and by UHT to produce a product stored at room temperature for 6 months. Results showed stable levels of oxidation, high physical stability, no microbial growth and a positive trend of sensory response during the period analyzed for UHPH soymilk. Moreover, the UHPH system was designed to work at continuous flow, allowing its application in several industrial food processes.