Effect of high pressure thermal sterilization on the formation of food processing contaminants

The use of high pressure thermal sterilization (HPTS) as an emerging technology for the sterilization of foods could be a big turning point in the food industry. HPTS can result in a better overall food quality, lower thermal load applied to the product and less unwanted food processing contaminants (FPCs) as e.g. furan and monochloropropanediol/-esters.Hence, within the EU FP7 founded Prometheus-project HPTS treatments were performed for selected food systems. Therefore, two spore strains were tested, the Geobacillus stearothermophilus and the Bacillus amyloliquefaciens, in the temperature range from 90 to 121 °C at 600 MPa. The treatments were carried out in different fish system and ACES-buffer. The treatment at 90 and 105 °C showed that the G. stearothermophilus is more pressure sensitive than the B. amyloliquefaciens. The formation of FPCs was monitored during the sterilization process and compared to the amounts found in retorted samples of the same food systems. Depending on the food system the amounts of furan could be reduced between 71 and 97% for the tested temperature pressure combination even at sterilization conditions of F₀-value 7 min.Industrial relevanceThe high pressure thermal sterilization (HPTS) process is an emerging technology to produce high quality low acid food products, which are shelf-stable at ambient temperature. In addition the consumer today demands foods which are minimally processed and are healthy and safe. However, an industrial scale process has not yet been implemented.The work in this paper shows different temperature combinations (90 to 121 °C) at 600 MPa and their influence on the endospore inactivation and also on the formation of unwanted food process contaminants (FPCs), such as furan and monochloropropanediol/-esters, in comparison to retorting. The use of HPTS could lead to shorter process times and a means by which a better quality of the foods could be achieved.     

Pressure–ohmic–thermal sterilization: A feasible approach for the inactivation of Bacillus amyloliquefaciens and Geobacillus stearothermophilus spores

The efficacy of a pressure–ohmic–thermal sterilization (POTS) for Bacillus amyloliquefaciens and Geobacillus stearothermophilus spore inactivation was investigated. Spores (2.5 × 10⁸ cfu/ml) were inoculated in 0.1% NaCl solution (pH 5.0 and 7.0), green pea puree (pH 6.1), carrot puree (pH 5.0) or tomato juice (pH 4.1). Samples were ohmically (50 V/cm) treated at 600 MPa and 105 °C for various holding times using a laboratory-scale high-pressure processor. B. amyloliquefaciens and G. stearothermophilus spores suspended in 0.1% NaCl solution (pH 7.0) were inactivated by 4.6 and 5.6 log, respectively, for a 30-min holding time. B. amyloliquefaciens and G. stearothermophilus spores in tomato juice were reduced by 3.1 and 4.8 log, respectively, for a 10-min holding time. Spore germination was highest in the G. stearothermophilus suspended in 0.1% NaCl solution (pH 7.0). POTS treatment appears to be a potent method for inactivating pressure–thermal resistant bacterial spores.Industrial RelevanceFood industry is interested in developing superior quality low-acid shelf-stable foods. This study evaluated the pressure–ohmic–thermal sterilization (POTS) for the inactivation of Bacillus amyloliquefaciens and Bacillus stearothermophilus endospores. The impact of food matrices and acidity on the spore resistance was also investigated. Knowledge gained from the study will help the food processors for understanding the importance of various POTS treatment parameters for sterilization of low-acid foods.     

Effect of enterocin EJ97 against Geobacillus stearothermophilus vegetative cells and endospores in canned foods and beverages

Geobacillus stearothermophilus is a thermophilic bacterium typically responsible for the flat-sour spoilage of low-acid canned food with high water activity. Control of vegetative cells and spores of G. stearothermophilus strains CECT 48 and CECT 49 by enterocin EJ97 produced by Enterococcus faecalis EJ97 is described. Both strains were highly sensitive to EJ97 in a culture medium. In samples from canned foods inoculated with a cocktail of vegetative cells or endospores of the two strains and stored at 45 °C for 30 days, viable cell counts were reduced below detection levels. The time course of microbial inactivation depended on the food sample and bacteriocin concentration. Dormant endospores were resistant to EJ97 short-time treatments (5 min), but endospores activated to germinate by heat became bacteriocin sensitive. The simultaneous application of enterocin EJ97 and heat treatments (90 and 95 °C) on dormant endospores had an increased antimicrobial effect that depended both on the bacteriocin concentration and the heat temperature. Results from this study strengthen the potential of enterocin EJ97 for biopreservation against G. stearothermophilus in canned vegetable foods and drinks.     

Isolation and identification of high pressure‐resistant bacteria naturally contaminating strawberry pulp

The inactivation of bacteria naturally present in strawberry pulp was investigated after high hydrostatic pressure (HHP) treatment at pressure levels up to 600 MPa at 25 °C for 5 ~ 25 min. Five strains of pressure‐resistant bacteria designated as A, B, C, D and E were isolated and identified. The five strains were gram‐positive, spore‐forming, rods or rod in chains. Growth of the strains was observed at 30 ~ 45 °C, and strain B also grew well at 55 °C. They could produce acid from glucose and were catalase‐positive. Analysis of 16S rRNA gene sequences showed that the five strains belonged to the genus Bacillus. Strain A and D exhibited the greatest 16S rRNA gene sequence similarity of 99% with B. licheniformis and B. firmus, respectively. By combination of phenotypic characteristics and 16S rRNA gene sequences, strain C was B. mycoides and E was B. pumilus. On the basis of physiological and biochemical characteristics, gyrB gene sequences analysis and whole‐cell fatty acids analysis, strain B was B. amyloliquefaciens. Further studies showed that strain B (B. amyloliquefaciens) exhibited the highest pressure resistance, and it was reduced by 4.62‐log after treatment at 600 MPa for 25 min at 25 °C as the most effective observed inactivation.     

Unlocking Potentials of Microwaves for Food Safety and Quality

Microwave is an effective means to deliver energy to food through polymeric package materials, offering potential for developing short‐time in‐package sterilization and pasteurization processes. The complex physics related to microwave propagation and microwave heating require special attention to the design of process systems and development of thermal processes in compliance with regulatory requirements for food safety. This article describes the basic microwave properties relevant to heating uniformity and system design, and provides a historical overview on the development of microwave‐assisted thermal sterilization (MATS) and pasteurization systems in research laboratories and used in food plants. It presents recent activities on the development of 915 MHz single‐mode MATS technology, the procedures leading to regulatory acceptance, and sensory results of the processed products. The article discusses needs for further efforts to bridge remaining knowledge gaps and facilitate transfer of academic research to industrial implementation.     

Multiplex PCR for rapid detection of thermophilic Moorella thermoaceticaand Geobacillus stearothermophilus from canned foods and beverages

A multiplex PCR assay was developed to simultaneously detect the thermophilic spore‐forming bacteria Geobacillus stearothermophilus and Moorella thermoacetica, which are major sources of spoilage in the canned food and beverage industries because of their thermophilic persistence. A total of 294 samples were examined, and none of the samples demonstrated signs of spoilage. Culture‐based assays showed that forty‐five M. thermoacetica isolates were obtained, which was confirmed by multiplex PCR, and G. stearothermophilus was not detected in any of the canned food and beverage, but multiplex PCR analysis identified this species in almost all of the samples. Meanwhile, twelve Bacillus subtilis isolates were found under both aerobic and anaerobic conditions. Multiplex PCR may allow selective detection of species that are present at low levels in complex matrices, or those that cannot be detected by culture‐based methods. Screening for spoilage‐causing micro‐organisms in ingredients and samples from processing lines, together with traditional culture methods, will help risk management and improve hygiene control.     

Green Pea and Garlic Puree Model Food Development for Thermal Pasteurization Process Quality Evaluation

Development and selection of model foods is a critical part of microwave thermal process development, simulation validation, and optimization. Previously developed model foods for pasteurization process evaluation utilized Maillard reaction products as the time–temperature integrators, which resulted in similar temperature sensitivity among the models. The aim of this research was to develop additional model foods based on different time–temperature integrators, determine their dielectric properties and color change kinetics, and validate the optimal model food in hot water and microwave‐assisted pasteurization processes. Color, quantified using a^* value, was selected as the time–temperature indicator for green pea and garlic puree model foods. Results showed 915 MHz microwaves had a greater penetration depth into the green pea model food than the garlic. a^* value reaction rates for the green pea model were approximately 4 times slower than in the garlic model food; slower reaction rates were preferred for the application of model food in this study, that is quality evaluation for a target process of 90 °C for 10 min at the cold spot. Pasteurization validation used the green pea model food and results showed that there were quantifiable differences between the color of the unheated control, hot water pasteurization, and microwave‐assisted thermal pasteurization system. Both model foods developed in this research could be utilized for quality assessment and optimization of various thermal pasteurization processes.     

High-pressure and temperature effects on the inactivation of Bacillus amyloliquefaciens,alkaline phosphatase and storage stability of conjugated linoleic acid in milk

Milk rich in conjugated linoleic acid (CLA, 42 ± 3 mg g^− 1 fat) was used to evaluate the impact of high-pressure sterilization (HPS). The pressure, temperature and time needed to reduce 7-log of Bacillus amyloliquefaciens endospores were determined in the presence of nisin (4–64 mg L^− 1). In addition, the inactivation of alkaline phosphatase was evaluated. After HPS treatment, the remaining CLA and formation of hydroperoxides were monitored during storage up to 60 d at 25 °C. The addition of nisin (≥ 16 mg L^− 1) to milk significantly enhanced the inactivation of B. amyloliquefaciens (7-log reduction) after treatment at 600 MPa, 120 °C and 5 min of holding time. These conditions were selected to evaluate the impact of HPS on the CLA retention and hydroperoxides formation. Milk with the addition of nisin and treated with HPS delivered higher retention of CLA and a lower concentration of hydroperoxides compared with the UHT equivalent process (125 °C/15 s and 135 °C/10 s).Industrial relevanceHigh-pressure sterilization is a valuable alternative to produce superior quality milk products in cases where traditional thermal treatments have failed. This study evaluated the impact of processing conditions on the conjugated linoleic acid content at conditions where commercial sterilization has been achieved (7-log reduction of B. amyloliquefaciens). The outcomes of this study are considered as a step further for the development of high-pressure sterilized milk.     

Clostridium sporogenes-ATCC 7955 Spore Destruction Kinetics in Milk Under High Pressure and Elevated Temperature Treatment Conditions

Clostridium sporogenes (ATCC 7955) spores inoculated in milk (2% fat) were subjected to high-pressure (HP) treatments (700–900 MPa) and at elevated temperatures (80–100 °C) for selected times up to 32 min. Samples were sealed in 1-mL plastic vials and placed in a specially constructed insulated chamber to prevent temperature drop during the treatment. Both pressure pulse (with no hold time) and pressure hold techniques were employed for treatment. Pressure pulse resulted in a small, but consistent, destruction (up to 0.5 log kill) of spores. During the pressure hold treatment, the destruction followed a first-order model (R ² > 0.90). The kinetic data were compensated for the small variations in temperature during the treatment. As expected, higher pressures and higher temperatures resulted in a faster rate of spore destruction. Temperature-corrected D values ranged from 13.6 to 2.4 min at 700 MPa and 7.0 to 1.3 min at 900 MPa, respectively, with process temperatures set at 90 and 100 °C. In comparison, thermal treatments gave D values ranging from 156 min at 90 °C to 12.1 min at 100 °C. The temperature sensitivity Z _P values (16.5 to 20.3 °C) under high pressure (700–900 MPa) were higher than under conventional thermal processing (9.0 °C), indicating the spore’s thermal resistance to increase at HP processing conditions. The pressure sensitivity Z _T values varied between 450 and 680 MPa under the elevated temperature (80–100 °C) processing conditions. Overall, C. sporogenes 7955 spores were relatively more sensitive to temperature than pressure.     

Effect of thermal and high pressure processing on antioxidant activity and instrumental colour of tomato and carrot purées

Total antioxidant activity, levels of bio-active compound groups and instrumental colour of tomato and carrot purée subjected to high pressure treatment (400–600 MPa/15 min/20 °C) and thermal treatments (70 °C/2 min) were measured. Antioxidant activity in tomato and carrot purée was significantly higher (p < 0.05) than in untreated or thermally processed samples. High pressure treatments at 600 MPa retained more than 90% of ascorbic acid as compared to thermal processing in tomato purées. Heat treatments caused a rapid decrease in ascorbic acid (p < 0.05). Phenolic contents were in general un-affected by thermal or high pressure treatments. Colour parameters were significantly affected (p < 0.05) by thermal and high pressure processing. Principal component analysis (PCA) revealed that the first two components represented 97% and 92% of the total variability in instrumental colour parameters with respect to processing for tomatoes and carrots respectively.Industrial relevanceThis research paper provides scientific evidence of the potential benefits of high pressure processing in comparison to thermal treatments in retaining important bioactive compounds. Antioxidant activity (ARP), ascorbic acid, and carotenoids after exposure to high pressure treatments (400–600 MPa) were well retained. Our results also show that redness and colour intensity of purées were better preserved by high pressure processing than conventional thermal treatment. It would appear from a nutritional prospective, high pressure processing is an excellent food processing technology which has the potential to retain compounds with health properties in foods. Therefore high pressure processed foods could be sold at a premium over their thermally processed counterparts as they will have retained their fresh-like properties.     

Impact of Ionizing Radiation and Thermal Treatments on Furan Levels in Fruit Juice

The formation of furan in freshly prepared apple and orange juices as affected by ionizing radiation and thermal treatments was studied using a newly developed solid‐phase microextraction method coupled with gas chromatography‐mass spectrometry (GC‐MS). Results show that furan levels increased linearly as radiation dose increased from 0 to 5 kGy. Irradiation induced more furan in apple juice than in orange juice. During post‐irradiation storage at 4 °C, furan levels increased in both apple and orange juices, particularly in the 1st 3 d. On the other hand, irradiation degraded deuterated furan (d₄‐furan) spiked in water and fruit juices. The rate of degradation as a function of radiation dose was the highest in water and the lowest in orange juice. Submerging the juice samples in boiling water for 5 min induced higher amounts of furan in orange juice than in apple juice, but autoclaving (121 °C, 25 min) resulted in more furan formation in apple juice than in orange juice. Results reported here suggest that both ionizing radiation and thermal treatments induce furan formation in fruit juices.     

Original article: Modelling the effects of food ingredients and pH on high‐pressure processing inactivation of Bacillus cereus spores: a laboratorial study

The combination of high pressure and heat on Bacillus cereus spores in food matrix was investigated with the purpose of achieving a predictive model of microbial inactivation. The high‐pressure processing (HPP) conditions were fixed at 540 MPa and 71 °C for 16.8 min, which were determined as the optimum conditions considering six‐log‐cycle reductions of B. cereus spores. The effects of soybean protein, sucrose, soybean oil and pH on the inactivation of B. cereus spores by HPP were evaluated, and a quadratic predictive model for the effects of food ingredients and pH on the reductions of B. cereus spores by HPP was built using response surface methodology. The experimental results showed that soybean protein, sucrose and pH significantly affected the reductions of B. cereus spores. The predictive model is significant, because the level of significance was P < 0.0001 and the calculated F‐value is much greater than the tabulated F‐value. The adequacy of the predictive model equation was verified effectively using the experimental test data that were not used in the development of the model.     

食品非热力杀菌新技术

综述了国内外食品非热力杀菌的新技术 ,特别介绍了微生物抑制剂、等离子体杀菌、高压脉冲电场杀菌、超高压灭菌技术对杀菌效果的影响因素。这些技术有望部分取代现有的食品热杀菌技术。     

食品工业中超高压灭菌技术

该文介绍超高压杀菌原理、超高压技术处理食品特点、超高压灭菌与传统灭菌技术比较及超高压灭菌技术应用。     

Comparison of volumetric and surface decontamination techniques for innovative processing of mealworm larvae (Tenebrio molitor)

For food and feed safety of edible insects, effective decontamination methods need to be evaluated and developed. Traditional decontamination and preparation methods were reviewed and thermal and innovative inactivation methods for the decontamination of mealworm larvae were evaluated and compared. The impact of the surface decontamination techniques direct and indirect plasma treatment, and of volumetric methods such as high hydrostatic pressure treatment (400, 500, and 600 MPa) and thermal treatments (45 °C and 90 °C) for up to 15 min on the surface microbial load and on the overall microbial count of mealworm larvae (Tenebrio molitor) have been investigated. It was found that the indirect plasma treatment was an effective means for the surface decontamination of mealworm larvae, whereas high hydrostatic pressure at 600 MPa and thermal treatments in a water bath at 90 °C in comparison resulted in the highest reduction of the overall count. It is thus concluded that volumetric methods are favorable for the inactivation of the gut microbiota of insects.Industrial relevanceEdible insects represent a valuable alternative protein source that could contribute to food and feed security and are industrially mainly unexploited. For a successful marketing of edible insects food and feed safety has to be ensured and effective decontamination methods need to be developed.     

Response of Spores to High‐Pressure Processing

ABSTRACT: This review focuses on the responses of microbial spores to food processes that incorporate high hydrostatic pressures. While the majority of information deals with spores of Bacillus species, spores of Clostridium and Alicyclobacillus species are also discussed, and a section of the review surveys the responses of fungal spores to high‐pressure processing. The mechanisms of the germination of bacterial spores are outlined in detail with regard to spore physiology and structure, along with molecular aspects of germinants and the interaction with spore receptors. Use of treatments combining pressure and temperature for a range of different food products is reviewed, including examples of hurdle technology employing high hydrostatic pressure. Pressure‐assisted thermal sterilization is also discussed.     

Impact of enzyme inactivation conditions during the generation of whey protein hydrolysates on their physicochemical and bioactive properties

The thermal inactivation conditions (75 °C × 35 min, 80 °C × 10 min, 85 °C × 5 min and 90 °C × 5 min) for Protamex? following bovine whey protein concentrate (WPC) hydrolysis was studied with the view to limiting WPC hydrolysate (WPH) aggregation while maintaining bioactivity. A decrease in the amount of large WPH aggregates formed was observed at inactivation temperatures ≤85 °C. However, the WPC appeared to be more hydrolysed on heating at 75 °C × 35 min, as Protamex? was active for longer under these heating conditions. Significantly (P < 0.05), higher WPH antioxidant (oxygen radical absorbance capacity – ORAC) activity was obtained on inactivation at temperatures ≤80 °C. In contrast, the dipeptidyl peptidase IV (DPP‐IV) inhibitory properties of all WPH samples were similar (P > 0.05). A reduction in thermal treatment from 90 °C × 5 min to 85 °C × 5 min was sufficient to decrease the amount of large aggregates formed in the hydrolysate without altering its bioactive properties.     

Impact of high pressure processing on total antioxidant activity,phenolic, ascorbic acid,anthocyanin content and colour of strawberry and blackberry purées

The present study was undertaken to assess the effect of high pressure treatments and conventional thermal processing on antioxidant activity, levels of key antioxidant groups (polyphenols, ascorbic acid and anthocyanins) and the colour of strawberry and blackberry purées. Bioactive compounds (cyanidin-3-glycoside, pelargonidin-3-glucoside, ascorbic acid) and antioxidant activity were measured in strawberry and blackberry purées subjected to high pressure treatment (400, 500, 600 MPa/15 min/10–30 °C) and thermal treatments (70 °C/2 min). Samples were assessed immediately after processing. Different pressure treatments did not cause any significant change in ascorbic acid (p > 0.05). In contrast, following thermal processing (P₇₀ ≥ 2 min) ascorbic acid degradation was 21% (p < 0.05) as compared to unprocessed purée. However, no significant changes in anthocyanins were observed between pressure treated and unprocessed purées (p > 0.05), whereas conventional thermal treatments significantly reduced the levels (p < 0.05). In general, antioxidant activities of pressure treated strawberry and blackberry purées were significantly higher (p < 0.05) than in thermally processed samples. Colour changes were minor (ΔE) for pressurised purées but the differences were slightly higher for thermally treated samples. Redness of purées was well retained in high pressure treated samples. Therefore processing strawberry and blackberry by high pressure processing could be an efficient method to preserve these products quality. Hence high pressure processing (HPP) at moderate temperatures may be appropriate to produce nutritious and fresh like purées.Industrial relevanceThis research paper provides scientific evidence of the potential benefits of high pressure processing in comparison to thermal treatments in retaining important bioactive compounds. Antioxidant activity (ARP), ascorbic acid, and anthocyanins after exposure to high pressure treatments (400–600 MPa) were well retained. Our results also show that redness and colour intensity of strawberry and blackberry purées were better preserved by high pressure processing than conventional thermal treatment. From a nutritional perspective, high pressure processing is an attractive food preservation technology and offers opportunities for horticultural and food processing industries to meet the growing demand from consumers for healthier food products. Therefore high pressure processed foods could be sold at a premium than their thermally processed counterparts as they will have retained their fresh-like properties.     

A time temperature integrator for particulated foods: thermal process evaluation

 A time temperature integrator (TTI) was developed by immobilizing Bacillus stearothermophilus spores in a cylindrical particle consisting of an alginate-starch-mushroom purée. The particle showed homogeneous spore distribution, and when heated over a temperature range of 121 – 130° C negligible spore leakage was observed after the thermal process. The experimental data on spore survivor levels obtained for each temperature-time combination were compared with theoretical predictions using a mathematical model. The results showed a good correlation between the experimental and theoretical data. All these results provide evidence that this artificial particle could be a very reliable TTI for monitoring the thermal impact on micro-organisms during validating sterilization processes in continuous aseptic systems. Received: 25 February 1997     

食品非热杀菌技术

食品非热杀菌技术系指不使用热能杀死食品中微生物,最大限度保持食品原有营养、质构、色泽和风味的一类新型杀菌技术;该文重点介绍超高压杀菌、高压脉冲电场杀菌、等离子体杀菌、紫外线杀菌、臭氧杀菌等非热杀菌技术原理、特点及其在食品工业中应用。