Survival and growth behavior of common foodborne pathogens in falafel paste under different storage temperatures.

Falafel is a popular breakfast food in the Middle East that has been recently involved in several outbreaks of foodborne illnesses. The aim of the study was to explore the growth behavior of Salmonella enterica, Escherichia coli O157:H7, Shigella sonnie, Shigella flexneri, Listeria monocytogenes and Staphylococcus aureus in falafel paste (FP) under different storage temperatures (4, 10, or 24 °C) for 14 days. FP (pH = 6.2, aw = 0.96) was inoculated with 5.0 to 6.0 log CFU/g of each of the pathogens separately. Salmonella spp. significantly declined by 1.5 log at 4 °C but grew significantly by ca. 2 and 4 log at 10 and 24 °C, respectively after 14 days. E. coli O157:H7 significantly increased (4.5 log) in FP when stored under 24 °C and survived at a level of ~105 CFU/g at 10 °C. Comparatively, Sh. sonnie and Sh. flexneri showed a better survival pattern in FP stored under 4 °C and grew (˃ 3 log) after 5 days at 10 and 24 °C. L. monocytogenes was capable of growing by 1.9 and 4.3 log after 14 d days and by 3.9 log after 3 days at 4, 10, or 24 °C, respectively. No significant decline in S. aureus counts at 4 and 10 °C occurred, however, it increased significantly to ˃ 7 log CFU/g at 24 °C. Total mesophilic count and yeast and mold count reached to spoilage levels (˃107 CFU/g) in un-inoculated FP after 1 and 3 days of storage at 24 and 10 °C, respectively. FP could support the growth of common foodborne pathogens and hence it is recommended to utilize natural antimicrobials in FP and keep the product under refrigeration (4 °C) to preclude the growth of vegetative foodborne pathogens.

Heat-induced formation of advanced glycation end-products in ground pork as affected by the addition of acetic acid or citric acid and the storage duration prior to the heat treatments.

The heat-induced (121 °C, 10 or 30 min) formation of two potentially hazardous advanced glycation end-products (AGEs), protein-bound Nɛ -carboxymethyllysine (CML) and Nɛ -carboxyethyllysine (CEL), in pork as affected by citric or acetic acid (0.5, 1 g/100 pork) and the storage duration (0 °C, 0 - 8 d) prior to the heating was investigated. A longer storage time of raw pork resulted in higher levels of AGEs produced during the later heating, likely due to the accumulation of some AGE precursors during the storage. Depending on the acid level and heating time, adding acid in pork led to 30 - 54% (citric acid) or 14 - 48% (acetic acid) average reduction of heat-induced production of CML/CEL, which corresponded to the reduction of thiobarbituric acid reactive substances and Schiff bases. The marinating time of raw pork with an acid did not significantly affect (P = 0.959 - 0.998) the acid's inhibition effect on heat-induced formation of CML/CEL.

Smart traceability for food safety.

Current food production faces a tremendous challenge due to the growing human population. The global population is estimated to reach 9 billion by 2050 with 70% more food being required. Safe food is an important dimension of food security, and food traceability across the supply chain is a key component of this. However, current food traceability systems are challenged by frequent occurrences of food safety incidents and food recalls that have damaged consumer confidence, caused huge economic loss, and put pressure on food safety agencies. This review focuses on smart food traceability that has the potential to significantly improve food safety in global food supply chains. The basic concepts and critical perspectives for various detection strategies for food safety are summarized, including portable detection devices, smart indicators and sensors integrated on food packages, and data-assisted whole-genome sequencing. In addition, new digital technologies, such as Internet-of-things (IoTs) and cloud computing, are discussed with the aim of providing readers with an overview of the exciting opportunities in smart food traceability systems.

Formation of protein-bound Nε-carboxymethyllysine and Nε-carboxyethyllysine in ground pork during commercial sterilization as affected by the type and concentration of sugars.

This research was aimed to investigate the formation of protein-bound Nε-carboxymethyllysine (CML) and Nε-carboxyethyllysine (CEL) in ground pork at 121 °C (5-30 min) as affected by sugars (1-9% w/w, glucose, fructose, lactose, and sucrose).The addition of reducing sugar significantly (P < 0.05) increased the levels of CML and CEL in heat treated pork samples. Even adding 1% of glucose in pork could lead to 3.8 and 4.0 times increase in the formation rate constant (zero-order) of CML and CEL, respectively. In a typical commercial sterilization process (121 °C, 30 min), adding glucose, fructose or lactose in pork resulted in an average increase of 224-581%, 26-276%, and 8-189% CML, and 217-720%, 213%-15.8 times, and 20-150% CEL, respectively, depending on the sugar concentration. Sucrose did not promote the formation of CML and CEL in pork during heating.

Trace analysis of organic compounds in foods with surface-enhanced Raman spectroscopy: Methodology, progress, and challenges.

Surface-enhanced Raman spectroscopy (SERS) provides a potential solution for rapid analysis of trace compounds such as residual pesticides, naturally occurred toxicants, banned or restricted drugs, and food additives in complex food matrices. In this review, the basic principles of SERS and general approaches to successfully apply SERS in food analysis are covered from an applications perspective. The key steps including substrate selection and evaluation, sample preparation and simplification, spectral collection, and data analysis during the development of SERS methods for food analysis are summarized, together with the discussion of typical underlying technical barriers or major challenges of these methods and their applications. Future directions in successfully applying SERS technology as a routine analytical approach to solve real-world food problems are analyzed. This comprehensive review summarizes the recent progress on theory, application, and scope of SERS for food analysis, providing a basic understanding of the technology; more importantly, key methodology, potential pitfalls, and possible solutions during the development of rapid SERS methods based on authors' years of SERS experience are shared with researchers in the field.

Development of an Oxygen Sensitive Model Gel System to Detect Defects in Metal Oxide Coated Multilayer Polymeric Films.

Metal oxide coated multilayered polymeric pouches provide a suitable alternative to foil-based packaging for shelf-stable products with extended shelf-life. The barrier performance of these films depends upon the integrity of the metal oxide coating which can develop defects as a result of thermal processing and improper handling. In this work, we developed a methodology to visually identify these defects using an oxygen-sensitive model gel system. Four pouches with different metal oxide coatings: MOA (Coated PET), MOB (SiOx -coated PET), MOC (Overlayer-AlOx -Organic-coated PET), MOD (Overlayer-SiOx -coated PET) were filled with water and retort-processed for 30 and 40 min at 121 °C. After processing, the pouches were cut open, dried and subsequently filled with a gel containing methylene blue that changes color in the presence of oxygen. The pouches were then stored at 23 and 40 °C for 180 and 90 days, respectively. Defects were identified by observing the localized color change from yellow to blue in the packaged gel. These observations were confirmed through measurement of oxygen and water vapor transmission rates, as well as SEM and CLSM analyses. The MOC pouches showed the least change in barrier properties after thermal processing. This was due to crosslinking in the organic coating and protection provided by the overlayer. The melting enthalpy of all films increased significantly (P < 0.05) after sterilization. This may increase the brittleness of the substrates after processing. Findings may be used to improve the barrier performance of metal oxide coated polymeric films intended for food packaging applications. PRACTICAL APPLICATION: In this study, we developed a methylene blue-based, oxygen-sensitive model gel system to identify defects in metal oxide coated polymeric structures induced by thermal processing and mechanical stresses. We also performed a comprehensive analysis of these defects through CLSM and SEM. The gel system and methodology developed may be useful in the design and development of high barrier metal oxide coated films.

Natural color pigments: oxidative stability and degradation kinetics during storage in thermally pasteurized vegetable purees.

BACKGROUND: Package oxygen transmission rate (OTR) can affect the stability of natural color pigments such as anthocyanins, betalains and chlorophylls in foods during storage. In the present study, we investigated the oxygen sensitivity of selected pigments in thermally pasteurized vegetable purees held at a refrigeration temperature. We modulated the oxygen ingress in packaging using multilayer films with OTRs of 1, 30 and 81 cm3  m-2  day-1 . Red cabbage, beetroot and pea purees were vacuum packed, pasteurized to achieve a cumulative lethality of P 90 ° C 10 ° C = 12.8-13.4 min and stored at 7 °C for 80 days. RESULTS: Anthocyanins were relatively stable (< 4% losses), regardless of the film OTR. Betalains showed the highest sensitivity to different OTRs, with total losses varying from 4% to 49% at the end of storage and showing significant differences (P < 0.05) among the three films. Chlorophylls showed no significant difference (P > 0.05) in sensitivity to film OTRs. However, continuous degradation of chlorophylls was observed for all film types, with total chlorophyll losses ranging from 33% to 35%. Overall color differences (ΔE) at the end of storage for cabbage, beet and pea puree were between 0.50-1.70, 1.00-4.55 and 7.41-8.08, respectively. Betalains and chlorophylls degradation followed first-order and fractional conversion kinetics, whereas ΔE followed zero-order and fractional conversion kinetics during storage. CONCLUSION: All three pigments behaved differently to oxygen ingress during storage. Low to medium barrier films are suitable for products containing red cabbage anthocyanins. High barrier films are must for betalains, whereas medium to high barrier films are suitable for chlorophyll-containing products. © 2019 Society of Chemical Industry.

Efficacy of Food Safety Training in Commercial Food Service.

Proper food safety training is essential to decrease incidences and overall rates of foodborne illnesses and outbreaks. Though many commercial restaurants should provide proper food safety training to food handler employees, this training is not always offered or effective. Here, we summarize the results of a primary literature study concerning the effectiveness of food safety training in commercial settings. The literature chosen for review contained only studies with experimental food safety training, with before and after training data. Through evaluation of these studies, the best practice for ensuring effective training and follow-through were the use of food safety training programs, which incorporated both knowledge and behavior-based training. PRACTICAL APPLICATION: Food safety managers in food service establishments may consider reevaluating their current food safety training program to incorporate behavioral-based food safety training in addition to knowledge-based training.

Fiber-Rich Food Processing Byproducts Enhance the Expansion of Cornstarch Extrudates.

Expansion characteristics of cornstarch-based extrudates incorporating fiber-rich food processing byproducts was explored. Waxy and regular cornstarch were used as the base materials with apple pomace and sugarcane bagasse incorporated at two addition levels (0%, 15%, and 30% w/w). Extrusions were conducted at three different screw speeds (150, 200, and 250 rpm) with other parameters optimized and kept constant. Apple pomace inclusion resulted in higher initial expansion index (4.23 to 5.60) and higher stable expansion index (2.76 to 4.43), but also showed higher shrinkage (8.50% to 34.72%) than sugarcane bagasse extrudates at the same inclusion levels. Inclusion of apple pomace showed potential of producing extrudates with significantly higher expansion than cornstarch control, with relatively lower energy inputs. Extrusion methods used here have the potential to preserve the textural quality and nutritional value of the fiber-enriched extrudates, providing the base for healthier snack food items. PRACTICAL APPLICATION: Findings from this study can be extended to the other fiber-rich food processing byproducts, such as other fruit and vegetable pomace, cereal brans, and pulse hulls among other materials. This data will help the development of fiber-enriched extruded snacks that would have favorable consumer traits.

Effect of storage time and temperature on the viability of E. coli O157:H7, Salmonella spp., Listeria innocua, Staphylococcus aureus, and Clostridium sporogenes vegetative cells and spores in vacuum-packed canned pasteurized milk cheese.

The effect of storage temperature and time on the viability of several foodborne bacterial pathogens inoculated into vacuum-packed canned pasteurized cow's milk cheese was investigated. Three popular cheese styles namely, a semi-soft white Monterey Jack style cheese, and two Cheddar cheeses vacuum packaged in mason jars were inoculated with a 3-strain cocktail of each of the following microbes at the mean concentrations listed: Escherichia coli O157:H7 (6.6 log CFU/g), Salmonella spp. (6.3 log CFU/g), Listeria innocua (6.4 log CFU/g), Staphylococcus aureus (3.6 log CFU/g), and Clostridium sporogenes vegetative cells (6.3 log CFU/g), and spores (6.0 log CFU/g). The effect of storage temperature (at 4.4, 10, and 21.1 °C) and the time (from 0 to 365 days) on the survival of the inoculated organisms was evaluated at different sampling times (0, 30, 60, 120,180, and 365 days). Both storage temperature and the time had a significant effect on the viability of the test organisms. Increasing the storage temperature from 4.4 to 21.1 °C and the storage time for up to 365 days increased pathogen reduction. The type of cheese also had a significant effect on the viability of the test organisms. At the same sampling times, the viability of E. coli O157:H7 and Salmonella spp., were highest in Monterey Jack-style cheese followed by the Cheddar cheeses one to which annatto had been added (Cheddar 1) and the second, a white Cheddar that has an added adjunct flavor culture (Cheddar 2). Similarly, the type of cheese and the time-temperature conditions to which the cheese was exposed had a significant effect on the viability of L. innocua. Among the tested organisms, S. aureus was most susceptible while C. sporogenes (both vegetative cells and spores) were most resistant. The findings of this challenge study indicate that vacuum packed canned cheese is not a favorable environment for the growth of bacterial pathogens. Depending upon the type of canned cheese, appropriate storage times and temperatures are critical to ensure microbiological safety.

Combination effects of salts and cold storage on the formation of protein-bound Nɛ-(carboxymethyl)lysine and Nɛ-(carboxyethyl)lysine in raw and subsequently commercially sterilized ground pork.

The effects of cold storage (0 °C, 0-8 days) and salts (NaCl, 0.5-5%; NaNO2, 50-150 mg/kg) on the formation of protein-bound Nɛ-(carboxymethyl)lysine (CML) and Nɛ-(carboxyethyl)lysine (CEL) in raw and subsequently commercially sterilized (121 °C, 10 min) pork were investigated. Based upon two-factor analysis of variance (α = 0.05), there was no significant interaction effect between salts and storage time on the levels of CML and CEL in raw or sterile pork; salts and storage time did not significantly affect the amounts of CML and CEL in raw pork. However, in sterile pork, 1.5-5% NaCl treatments led to an average of 7.5-52.6% increase in CML, while NaNO2 resulted in 25.4-37.1% and 21.4-23.4% reduction in CML and CEL, respectively; raw pork stored for 8 days led to 82.5% increase of CML and 32.6% increase of CEL in the sterile products (n = 30), as compared to those without cold storage.

Electrolyzed water and mild-thermal processing of Atlantic salmon (Salmo salar): Reduction of Listeria monocytogenes and changes in protein structure.

This study investigated the effect of different electrolyzed water (EO) solutions, including acidic electrolyzed water (AEW) and neutral electrolyzed water (NEW), alone and in combination with mild thermal processing (50, 55, 60, 65 °C) at different exposure times (2, 6, 10 min) on the reduction of Listeria monocytogenes on Atlantic salmon fillets. The effects of the EO water solutions on cell wall structures of L. monocytogenes and on the secondary structure of salmon protein were studied using Fourier Transform Infra-Red (FTIR) spectroscopy. Temperature and time significantly influenced the efficacy of the AEW and NEW. NEW has stronger antimicrobial properties as compared to AEW. The highest bacterial reduction was observed at 65 °C after 10 min for salmon treated with NEW, with a 5.6 log10 CFU/g reduction. Spectral features show that the secondary protein structures in salmon muscle treated with NEW were less affected than tissue treated with AEW as shown in a PCA model. In addition, the FTIR spectra for L. monocytogenes showed that the NEW and AEW affected cell wall properties differently; this might be due to the form of available chlorine in NEW and AEW and to AEW having a lower pH. In general, NEW showed better antimicrobial properties, particularly when combined with mild thermal processing than AEW and also caused less alteration in protein structure. The findings of this study may be used to improve the quality and safety of cured and smoked ready-to-eat fish products.

Gold Nanorods as Surface-Enhanced Raman Spectroscopy Substrates for Rapid and Sensitive Analysis of Allura Red and Sunset Yellow in Beverages.

Synthetic colorants in food can be a potential threat to human health. In this study, surface-enhanced Raman spectroscopy (SERS) coupled with gold nanorods as substrates is proposed to analyze allura red and sunset yellow in beverages. The gold nanorods with different aspect ratios were synthesized, and their long-term stability, SERS activity, and the effect of the different salts on the SERS signal were investigated. The results demonstrate that gold nanorods have a satisfactory stability (stored up to 28 days). SERS coupled with gold nanorods exhibit stronger sensitivity. MgSO4 was chosen to improve the SERS signal of sunset yellow, and no salts could enhance the SERS signal of allura red. The lowest concentration was 0.10 mg/L for both colorant standard solutions. The successful prediction results using SERS were much closer to those obtained by high-performance liquid chromatography for the sample in beverages. SERS combined with gold nanorods shows potential for analyzing food colorants and other food additives as a rapid, convenient, and sensitive method.

Composition and Physicochemical Characterization of Fiber-Rich Food Processing Byproducts.

A wide range of fiber-rich food processing byproducts from various sources have been proposed as value-added ingredients for producing healthier food products. Characterizing their composition and physicochemical properties is crucial to understand their potential uses. Eight fiber-rich byproducts from different sources were fractionated into 2 different particle-size ranges. Different (P ≤ 0.05) proximate composition and physicochemical properties (pasting properties, water-binding capacity, and oil-binding capacity) were exhibited by them. These properties enabled hierarchical cluster analysis and principal component analysis to group the byproducts into 3 different clusters by functionality and from this, assigned ingredients in each cluster to a potential end-uses. Some end use examples include, as a source of fat, protein, sugar, and insoluble fiber; and for uses as a thickening agent, water-binder, emulsion-enhancer, and fat-binder. PRACTICAL APPLICATION: The data presented in this study can be used by food manufacturers and product developers as the basis for choosing fiber-rich byproducts for specific applications and assist them in developing specific formulation and processing strategies. This characterization will reduce the time for development of fiber-rich foods, increasing industrial uses of byproducts, and decreasing food waste.

Vacuum impregnation of firming agents in red raspberries.

BACKGROUND: Red raspberries are a delicate and highly perishable fruit with a fragile pulp tissue. In this study we used vacuum impregnation (VI) methods to incorporate pectin and calcium chloride into whole red raspberries to improve their firmness. Specifically, we impregnated low methoxyl pectin (LMP) at 10 g of pectin kg-1 of solution and calcium chloride (CaCl2 ·2H2 O) at 30 g calcium kg-1 of pectin, and on the other side pectin methylesterase (PME) at 10 g of enzyme kg-1 of solution, and (CaCl2 ·2H2 O) at 10 g of calcium kg-1 of solution, into whole red raspberries. We tested three vacuum levels 33.9, 50.8, and 67.8 kPa, three vacuum impregnation times 2, 7, and 15 min, and two temperatures, 20 and 40 °C, during VI treatment. Maximum force (FM ) and gradient (GC3 ) were evaluated to assess raspberry firmness. RESULTS: A vacuum level of 50.8 kPa, processing time of 7 min, and a LMP and calcium infusion at 20 °C resulted in the firmest fruit compared to the other treatments. At these VI treatment conditions, FM and GC3 values of red raspberries obtained were 28 N, and 8.4 N mm-1 , respectively. CONCLUSION: The optimal VI conditions identified in this study can be used to improve firmness and structural integrity of red raspberries by infusion of LMP and calcium. Findings on vacuum-impregnated red raspberries may be used to develop dehydrofrozen berries for incorporation into bakery and dairy products. © 2018 Society of Chemical Industry.

Rapid and sensitive surface-enhanced Raman spectroscopy (SERS) method combined with gold nanoparticles for determination of paraquat in apple juice.

BACKGROUND: Paraquat, a highly efficient herbicide, is widely used in agricultural practices throughout the world. However, paraquat residues in food pose a threat to human health. In order to develop a rapid and sensitive method, surface-enhanced Raman spectroscopy (SERS) coupled with gold nanoparticles was applied to analysis of paraquat in apple juice. RESULTS: Natural organic compounds (sugars and organic acids) in apple juice interfered with SERS measurement. Sample preparation was needed. Paraquat could be detected at concentrations as low as 0.02 and 0.1 µg mL- 1 with the weak cation-exchange solid-phase extraction (WCX-SPE) method and dilution method for sample preparation, respectively. For quantitative analysis, the R2 cv of the partial least-squares regression model with the dilution method (0.939) was not as good as with the WCX-SPE method (0.984), but the dilution method is much less costly, simpler and time saving. Satisfactory recovery values were obtained ranging from 94.73% to 114.81%, with the exception of 56.55% for the lowest concentration. CONCLUSION: This work showed that SERS combined with gold nanoparticles could determine paraquat in apple juice. As a simple, rapid and ultrasensitive method, it has great practical potential for detection of other contaminants in a variety of foods. © 2018 Society of Chemical Industry.

Monitoring Shelf Life of Pasteurized Whole Milk Under Refrigerated Storage Conditions: Predictive Models for Quality Loss.

The shelf life of pasteurized milk is generally determined through microbiological analysis. The objective of this study was to correlate microbial quality parameters then to design predictive models for shelf life of pasteurized milk. We analyzed pasteurized milk (3.9% fat) for aerobic plate counts (APCs), psychrotrophic bacteria counts (PBCs), and Bacillus spp. counts at 5, 7, 10, 13, 15, and 19 (±1 °C) to the end of storage time. We also monitored titratable acidity, pH, and, lipase, and protease activity and correlated this with APC, which is the principal index defining shelf life. Results indicate that the shelf life of pasteurized milk was 24, 36, and 72 h at 19, 15, and 13 °C respectively, as determined by APC and acidity indicators. However, milk stored at lower temperatures of 5, 7, and 10 °C had longer shelf life of 30, 24, and 12 d, respectively. A sharp increase in titratable acidity, while decrease pH were observed when APCs reached 5.0 log10 CFU/mL at all storage temperatures. Lipase and protease activities increased with storage temperature. At 5 and 7 °C, however, protease activity was very low. Therefore, we eliminated this parameter from our quality parameters as a potential spoilage indicator. PRACTICAL APPLICATION: Findings of this research are useful for monitoring the quality of commercial pasteurized milk, particularly in locations where environmental conditions make longer storage difficult. The study also provides valuable information for development of colorimetric shelf life indicators.

Rheological and sensory behaviors of parboiled pasta cooked using a microwave pasteurization process.

Pasta hydration and cooking requirements make in-package microwave pasteurization of pasta a processing challenge. The objective of this study was to assess instrumental and sensory attributes of microwave-treated pasta in comparison to conventionally cooked pasta. Fettuccine pasta was parboiled for 0, 3, 6, 9, or 12 min, pasteurized by microwaves at 915 MHz, then stored under refrigeration for 1 week. Pastas were evaluated by a trained sensory panel and with rheometry. Total pasta heat treatment affected both rheological and sensory behaviors; these differences were attributed to ultrastructure differences. Significant nonlinear behavior and dominant fluid-like behavior was observed in all pastas at strains >1%. Sensory results suggested microwave pasteurization may intensify the attributes associated with the aging of pasta such as retrogradation. A clear trend between magnitude of heat treatment and attribute intensity was not observed for all sensory attributes tested. The microwave pasta with the longest parboil time showed rheological behavior most similar to conventionally cooked pasta. Principal component analysis revealed that no microwave-treated pasta was similar to the control pasta. However, pasta parboiled for 9 min before microwave treatment had the greatest number of similar sensory attributes, followed by pasta parboiled for 6 or 12 min. Further study is needed to determine overall consumer acceptance of microwave-treated pasta and whether the differences in sensory and rheological behavior would impact consumer liking. PRACTICAL APPLICATIONS: The results of this study may be applied to optimize microwave pasteurization processes for cooked pasta and similar products, such as rice. The measurement and analysis procedures can be used to evaluate processing effects on a variety of different foods to determine overall palatability.

Inhibition of Shigella sonnei and Shigella flexneri in Hummus Using Citric Acid and Garlic Extract.

Hummus (chickpea dip) is a ready-to-eat product that may pose a significant risk to human if pathogens are present. Several organisms including Shigella spp. have been isolated from hummus. However, studies on the survival and inhibition of Shigella spp. in food are scarce. This study investigated the growth pattern of Sh. sonnei and Sh. flexneri in hummus at different temperatures (4, 10, and 24 °C). Additionally, the inhibitory activity of different concentrations of citric acid (CA) (0.5%, 1.0%, and 2.0%) and garlic extract (GE) (1.0%, 2.0%, and 3.0%) against Sh. sonnei and Sh. flexneri inoculated into hummus and stored at 4 and 10 °C was investigated. Both Shigella spp. survived well at 4 °C, while both grew to >7.0 log10 after 4 d at 10 °C or 1 d at 24 °C. At 4 °C, CA at 0.5% and 1.0% resulted in a slight reduction in the count (approximately 1.0 log10 ); a complete elimination of Sh. sonnei was attained by using 2.0% CA. However, approximately 3.0 log10 reduction in Sh. sonnei was obtained at 10 °C. For Sh. flexneri, CA at 0.5% and 1.0% resulted in a bacteriostatic inhibition. GE at 1.0% and 2.0% resulted in approximately 1.0 to 2.0 log10 reduction in Sh. sonnei count at 4 °C, while at 3.0% GE, approximately 4.0 and 3.0 log10 reductions were obtained at 4 and 10 °C, respectively. In comparison, the 2.0% and 3.0% GE resulted in a bacteriostatic effect against Sh. flexneri at 4 and 10 °C.

Effect of inulin and glycerol supplementation on physicochemical properties of probiotic frozen yogurt.

The present study was designed to investigate the effects of inulin and glycerol supplementation on physicochemical properties of probiotic frozen yogurt. Frozen yogurt was prepared with different types of probiotic (Lactobacillus acidophilus and Bifidobacterium lactis) along with yogurt starter culture (Streptococcus thermophilus and Lactobacillus bulgaricus). The frozen yogurt mixture was supplemented with inulin (2%, 4%, and 6%) and glycerol (1%, 2%, 3%, and 4%). The results showed that inulin 4% and 6% supplementation increased the overrun by 3% and 5% and the glass transition temperature by 3.3% and 2.8%, and decreased the hardness by 7% and 11%, respectively. Inulin supplementation did not have a significant effect on ice crystal size (p > 0.05). Glycerol supplementation increased the stickiness from 2.4% to 18.7%, and decreased the hardness from 8.0% to 14.5% and the glass transition temperature from 2.4% to 34.5%, respectively. Glycerol supplementation did not have a significant effect on overrun or melting rate (p > 0.05).