Flavour profiles and survival of starter cultures of yoghurt produced from high-pressure homogenized milk

Volatile carbonyl compounds, organic acids and yoghurt bacteria counts were investigated in yoghurts made from ultra-high pressure homogenized milk. Yoghurts were manufactured from milk treated using ultra-high pressure homogenization at 200 or 300 MPa and at 30 °C or 40 °C, and compared with those produced from heat-treated milk with 3% added skim milk powder. To study the evolution of these parameters, samples were analysed after days 1, 14 and 28 of storage. Yoghurts from milk heat-treated or treated at 300 MPa had very similar profiles of organic acids and volatile compounds, as well as similar bacterial counts of both starter cultures. In comparison, yoghurts from milk treated at 200 MPa at either 30 °C or 40 °C gave different profiles, together with a sharp decrease in counts of lactobacilli. During storage, only slight differences in flavour compounds and yoghurt bacteria counts were detected, except in those samples from milk treated at 200 MPa.     

Modifying the microstructure of low-fat yoghurt by microfluidisation of milk at different pressures to enhance rheological and sensory properties

The effects of microfluidisation of milk at different pressures, prior to heat treatment, on structural and sensory properties of low-fat stirred yoghurt, were investigated. Low-fat yoghurts prepared from microfluidised milk were compared with low-fat (1.5%) and full-fat (3.5%) control yoghurts made with homogenised (20/5 MPa) milk. The microstructure of low-fat yoghurts prepared with microfluidised milk consisted of smaller and more uniform fat globules, well incorporated into more interconnected fat-protein gel networks, compared with those of control yoghurts. This modification in microstructure caused significant changes in gel particle size, sensory profile and rheological behaviour. Microfluidisation increased the gel particle size, gel strength and viscosity; marked beneficial effects were found at higher pressures (50–150 MPa). Microfluidising milk at 50–150 MPa increased the gel strength by 171–195% and viscosity by 98–103%, creating low-fat yoghurts with creaminess and desirable texture properties similar to, or better than, full-fat conventional yoghurt.     

Properties of low-fat stirred yoghurts made from high-pressure-processed skim milk

Physical properties of stirred yoghurt made from reconstituted skim milk that was high-pressure (HP)-treated at 100, 250 or 400 MPa, at 25, 70 or 90 °C, for 10 min, prior to inoculation with yoghurt cultures, were studied; portions of milk HP-treated at 25 °C were also heat-treated at 90 °C for 10 min before or after pressure treatment. Control yoghurts were made from skim milk given a heat treatment at 90 °C for 10 min. Fermentation time was not affected by treatment applied to the milk. HP treatment of skim milk at 25 °C, before or after heat treatment, gave stirred yoghurts of similar viscosities to that made from conventionally heat-treated milk. Lower viscosities were obtained when stirred yoghurts were made with milk HP-treated at elevated temperatures. A model is proposed to correlate properties of yoghurt with HP/heat-induced changes in interactions and structures of protein in the milk samples.Industrial relevanceTo meet end user expectations, the dairy industry needs to diversify its product range by tailoring specific functionalities. To meet these expectations, new processing methods such as high-pressure processing are of interest for their potential to achieve specific and/or novel functionalities and/or improve efficiencies, including reduced chemical and water use. In this paper, an investigation of the use simultaneous pressurization and heating of milk before the manufacture of stirred yoghurt is presented.     

Rheological properties of high-pressure-treated Gouda cheese

The rheological properties of high-pressure-treated (50–400 MPa, 1 h) and untreated Gouda cheese were compared. Immediately after pressure release, oscillation measurements gave lower storage and loss moduli from 50 MPa onwards. Simultaneously, tan δ was higher, indicating a relatively less solid-like behaviour of the pressurized samples. Creep measurements showed that samples treated at 400 MPa got less rigid, less solid-like, and more viscoelastic; from 50 MPa onwards, the samples had less resistance to flow at longer times. Texture profile analysis revealed that samples treated at 225 and 400 MPa showed no macroscopical breakage. Relaxation measurements gave a higher level of stress decay at long relaxation times and a higher rate at which the stress relaxes. During further ripening after pressure release, differences between pressure-treated and untreated samples became smaller. At 42 days of ripening, any or only a slight difference could still be observed. Dissolution experiments showed that hydrophobic interactions in Gouda cheese were weakened by pressure treatment. This possibly led to structural changes of the paracasein network causing the rheological property changes. These pressure effects on proteins in Gouda cheese are possibly reversible as hydrophobic interactions and rheological properties were restored during ripening.     

Antioxidant capacity,phenolic composition and microbial stability of aronia juice subjected to high hydrostatic pressure processing

The aim of this study was to characterize the effect of high hydrostatic pressure (200–600 MPa/15 min) and storage (4 °C/80 days) on aronia juice quality. The total antioxidant capacity, phenolic content and composition were assessed using an updated analytical strategy. Microbial growth was also analyzed following juice storage. Among all the analyzed juices, the untreated aronia juice had the greatest reduction (36%) in total polyphenols over the entire storage period. At the end of the storage period, the pressurized juices demonstrated ABTS and FRAP values higher by 14% and 5% as compared to the untreated juices. The main antioxidants identified in the aronia juice were: chlorogenic acid; neochlorogenic acid; cyanidin 3-galactoside; cyanidin 3-xyloside; cyanidin 3-arabinoside; cyanidin 3-glucoside. Cyanidin 3-glucoside was the most stable compound during juice storage. Microorganism growth in juices pressurized at 400–600 MPa was below the detection limit (< 1 CFU mL^− 1) upon storage.Industrial relevanceAronia berries are rarely consumed fresh since they give off several negative sensory attributes. Multiple health-promoting properties of aronia berries make them a valuable raw material for juice production. However, processing involves pasteurization or hot-filling strongly diminishes the product quality due to the changes in quantity and quality of thermolabile phytochemicals. The objective of this work was to characterize the effect of high hydrostatic pressure on the antioxidant capacity, polyphenol content and composition and microbial stability of aronia juice. Results of this study may be useful for the juice industry commercialize this technology for the development healthy, nonclarified aronia juices with desired level of quality.     

Rheological,microstructural and sensory characterization of low-fat and whole milk set yoghurt as influenced by inulin addition

The effect of inulin addition (0–4%) upon texture and microstructure of set yoghurt with different levels of fat (0.2%–3.5%) was investigated. A two-factor experimental design with four treatments was used for data analysis. Skimmed milk with various inulin and cream concentrations was standardized to 4% protein content, homogenized, heated to 92 °C and fermented at 42 °C until a pH of 4.6 was reached. The chemical composition, pH, consistency and microstructure properties of the yoghurts were analysed after 6 days of storage at 5 °C. The statistical analysis showed that inulin and fat significantly affected the rheological and sensory results. Higher yield stress, “firmness” and “creaminess” values were observed in yoghurt produced with higher inulin additions, whereas the pH value was not affected. A significant correlation was found between yield stress and sensory determined firmness (r = 0.91). The microstructure examined by confocal laser scanning microscopy (CLSM) was only slightly affected by the concentrations of inulin in the range studied, possibly due to weak protein interactions between the inulin and the milk protein network.     

Effect of high pressure,temperature, and storage on the color of porcine longissimus dorsi

The color of pork longissimus dorsi high pressure (HP) treated at 200 to 800 MPa at 5 and 20 °C for 10 min was determined to a high degree by pressure level and to a lesser degree by temperature. Severe color changes appeared up to a threshold pressure at 400 MPa. HP treatment at 20 °C compared to 5 °C resulted in meat, which was less red and slightly lighter. Storage at 2 °C for 6 days had no effect on lightness due to no further protein denaturation, but meat HP treated above 300 MPa became significantly less red and more yellow within the first day of storage. Reflectance spectra showed that a short-lived ferrohemochrome myoglobin species was formed during HP treatment at 300 to 800, but transformed into a brown, ferric form of the pigment within the first day of storage. This explains the observed changes in the redness and yellowness after one day of storage.     

Functional stability of gelatin–lignosulphonate films and their feasibility to preserve sardine fillets during chilled storage in combination with high pressure treatment

The physico-chemical and functional stability of gelatin (G) and gelatin–lignosulphonate (GLS) films stored during 4 weeks at 21 °C, (i) in container or (ii) in contact with oil, was examined. Addition of lignosulphonate dramatically increased ABTS radical scavenging and ferric ion reducing capacities, which remained practically unaltered after the storage period. GLS films exhibited reduced elongation at break, irrespective of storage medium, and retained their water resistance. The feasibility of using GLS film to improve the quality of sardine fillets during chilled storage, alone or in combination with high pressure treatment (300 MPa/10 min/7 °C), was evaluated. The combined use of GLS film with high pressure reduced microbial growth, total volatile basic compounds (TVB) and thiobarbituric acid reactive substances (TBARS) during chilled storage. No noteworthy high pressure-induced colour changes were observed in the sardine muscle using this treatment alone, although an increase in yellowness due to the combined treatment was detected.Industrial RelevanceAddition of lignosulphonate dramatically increased antioxidant properties (ABTS radical scavenging and ferric ion reducing) of gelatin films, which remained practically unaltered during 4 weeks of storage at room temperature. Application of those films confers stability during storage of chilled sardine, especially in combination with high pressure treatment. These novel packaging was promising for fish preservation.     

Microstructural and morphological behaviors of asparagus lettuce cells subject to high pressure processing

To explore the mechanisms of texture change under high pressure (HP) processing, the effects of different pressures on cell microstructure and cell morphological behaviors of asparagus lettuce were investigated using different microscopy approaches. Pectin immunofluorescence labeling was adopted to analyze cell morphological change in vivo by in situ visualization of cell wall. Image analysis showed that cells in asparagus lettuce treated at lower pressures (100 MPa, 200 MPa and 300 MPa) exhibited rounder and smaller than the untreated samples. However, the shapes of cells in asparagus lettuce treated at 500 MPa were close to the control. The in situ analysis on pectin distribution by CLSM indicated that pectin was mainly restricted in the corners of tricellular junctions in the samples treated at 200 MPa and 300 MPa, whereas pectin uniformly distributed around the whole cell wall at 500 MPa. The results of cell activity staining were consistent with that of ultrastructure change of cell wall and membrane observed by TEM, which suggested that plasma membrane was ruptured at the pressure of 200 MPa, 300 MPa and 500 MPa. Meanwhile, the integrity of cell wall structure was retained under all HP conditions. Based on the above results, a 7-cell tissue model has been proposed to show the cell morphological behavior. On the one hand, moderate HP (100 MPa–300 MPa) caused an initial texture loss of asparagus lettuce tissue, probably due to the loss of turgor pressure and the loose skeleton of cell wall. On the other hand, HP (500 MPa) caused less apparent texture loss of asparagus lettuce due to the unchanged pectin distribution, which can maintain the rigid and flexible cell wall.     

Probiotic stability of yoghurts containing Jerusalem artichoke inulins during refrigerated storage

Experimentally prepared Jerusalem artichoke inulins (JAI) were compared with two commercial chicory root inulins for their prebiotic potentials in media broth model and growth-sustaining ability in non-fat yoghurts. Experimental yoghurts were made with 12% reconstituted skim milk (RSM) supplemented with 4% inulin powders, inoculated with mixed cultures of Lactobacillus casei LC-01, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (1:0.5:0.5 based on supplier’s recommendation) and incubated overnight at 37 °C. Non-supplemented yoghurt was prepared from 16% RSM and used as control. The survival and acidifying activity of lactic and probiotic cultures in all yoghurts were investigated on weekly intervals during the shelf life of 28 days at 4 °C. Incorporation of JAI resulted in improved viability of LC-01, maintaining >7.0 log CFU/g during cold storage but did not affect the viability of yoghurt bacteria in comparison with the control.     

The effect of high hydrostatic pressure on the flow behaviour of skim milk–gelatin mixtures

The flow behaviour of aqueous solutions of gelatin, and skim milk–gelatin mixtures treated by high-pressure processing (HPP) were investigated. HPP was carried out at 5 °C for 15 min, at 150 MPa, 300 MPa, 450 MPa and 600 MPa, and the gelatin concentrations were varied from 0 to 1 wt.%. Viscosity measurements showed that the HPP treatment did not affect the flow behaviour of gelatin alone, nor that of the skim milk–gelatin mixtures made with < 0.4 wt.% gelatin. However, at gelatin concentration > 0.4 wt.%, the mixtures treated with 300 and 450 MPa exhibited a peculiar flow behaviour, where at intermediate shear rates the viscosity was higher than that of the non-treated mixture or the mixtures treated at 150 MPa and 600 MPa. Particle size measurements showed that for gelled mixtures (> 0.4 wt.% gelatin) 300 MPa HPP treatment resulted in an increase in the particle size, while at all other pressure treatments (> 150 MPa), a shift in particle size distribution to lower sizes was observed. Confocal microscopy showed that these skim milk–gelatin mixtures were phase-separated with a gelatin continuous phase, this was confirmed by dynamic rheological measurements which showed that qualitatively the viscoelastic properties of the mixtures were the same. A mechanism of the effect of high-pressure treatment on the casein micelle in skim milk–gelatin mixtures is proposed.Industrial relevanceThis fundamental work, dealing with the effect of high pressure on the physicochemical properties skim milk–gelatin mixtures could be relevant to the industry in several ways. Firstly, skim milk–gelatin mixtures are widely used in the dairy industry, particularly in yoghurt manufacture, where gelatine is used as a stabiliser. In addition the application of High Hydrostatic Pressure to such a system is also relevant, as this technology could be used as a substitute to the conventional heat treatment processes. Secondly, an important finding of this study is that under certain conditions of high pressure and gelatine concentration, an increase in viscosity is observed at intermediate shear-rate (between 10 and 100 s^?1). This is highly relevant to Industry if the system requires subsequent pumping. Thirdly, from a sensory view point, this range of shear rates (10 and 100 s^?1) is comparable to that experienced by a food bolus during swallowing. Thus, this effect of high pressure on the viscosity can influence sensory attribute of the skim milk–gelatin food system.     

Physicochemical and nutritional characteristics of blueberry juice after high pressure processing

This study was carried out to investigate the impact of high pressure processing (HPP) at different pressure (200, 400 and 600 MPa) and treatment times (5, 9 and 15 min) on ascorbic acid, total phenolics, anthocyanin stability and total antioxidant capacity, were also studied at different physicochemical parameters such as pH, °Brix and color. HPP treatments resulted in more than 92% vitamin C retention at all treatment intensities. On the other hand, total phenolic content in the juice was increased, mainly after HPP at 200 MPa for all treatment times. The total and monomeric anthocyanin were similar or higher than the value estimated for the fresh juice being maximum at 400 MPa/15 min (16% increase). Antioxidant capacity values were not statistically different for treatments at 200 MPa for 5–15 min in comparison with fresh juice, however for 400 MPa/15 min and 600 MPa for all times (8–16% reduction), the lowest values were observed for total antioxidant capacity determined with TEAC method. No significant changes were observed in pH and °Brix. Color changes (a*, b*, L* and ΔE) were not visually noticeable for pressurized beverage for all pressures and times.     

Effects of high pressure treatment on indigenous enzymes in bovine milk: Reaction kinetics,inactivation and potential application

High pressure-induced inactivation of the indigenous milk enzymes alkaline phosphatase (ALP), γ-glutamyltransferase (GGT) and phosphohexoseisomerase (PHI) was studied in the pressure range 400–800 MPa at temperatures between 5 and 40 °C. With respect to pressure stability the following ranking was observed: ALP>GGT>PHI. PHI was inactivated after pressure treatment at 500 MPa and 20 °C for 10 min. In terms of reaction kinetics, inactivation of GGT followed first-order reaction kinetics in the range of 400–800 MPa whereas a reaction order of 1.5 was found for ALP. Reactivation of pressure-treated ALP was observed at low enzyme activity resulting from severe pressure treatment and 2 h storage at 35 °C. The influence of process temperature on the pressure-induced inactivation of GGT and ALP was limited in the range 5–40 °C.     

Ultra high pressure homogenization of soymilk: Microbiological,physicochemical and microstructural characteristics

The effect of ultra high pressure homogenization (UHPH) at 200 and 300 MPa on soymilk was studied. A soymilk base product (BP) and ultra high temperature (UHT) treated soymilk were compared with UHPH treated soymilk. UHPH at 200 and 300 MPa reduced initial counts, spores and enterobacteria counts. Particle size analysis evidenced the intense reduction of particle size caused by UHPH, although the formation of aggregates was detected at 300 MPa. Colour differences between UHPH and BP or UHT soymilks were found. Treated soymilk (300 MPa) showed the lowest values of L¹, a¹ and b¹ coordinates. UHPH processed samples were more stable (showed less particle settling) than BP and UHT soymilks and these differences were also observed at days 30 and 60 of storage at 4 °C. Differential scanning calorimetry analysis indicated that soymilk proteins were partially denatured by 200 MPa, whereas UHPH treatment at 300 MPa showed the same extent of denaturation as UHT soymilk. Images of transmission electron microscopy showed the distribution and general characteristics of the colloidal particles and structures of UHPH, BP and UHT which were generally in accordance with the physicochemical parameters studied.     

Inactivation of hepatitis A virus,poliovirus and a norovirus surrogate by high pressure processing

Hepatitis A virus (HAV), feline calicivirus (FCV, a surrogate for non-culturable norovirus), and poliovirus (PV), suspended in buffered cell culture media, were treated with pressures ranging from 200 to 600 MPa at ambient temperature for between 30 and 600 s. HAV was inactivated by > 1-log₁₀ tissue culture infectious dose 50% mL^− 1 (TCID₅₀ mL^− 1) and > 2-log₁₀ TCID₅₀ mL^− 1 after 600 s treatment with 300 and 400 MPa, respectively, and was undetectable (> 3.5-log₁₀ TCID₅₀ mL^− 1 reduction) within 300 s treatment with 500 MPa. FCV was inactivated by 3.6-log₁₀ TCID₅₀ mL^− 1 after 120 s treatment with 300 MPa, and was undetectable after 180 s treatment with 300 MPa. PV was the most resistant with little or no substantial reduction in titre after 300 s treatment with 600 MPa. The studies were designed to determine the efficacy of using high pressure to inactivate enteric viruses and generate inactivation data to assist in determining appropriate process criteria for safe shellfish production.Industrial relevanceThe high pressure treatment of raw oysters has proved commercially successful, due in part to a marked increase in the product’s shelf life, yet little alteration of its organoleptic properties. Illnesses from human enteric viruses such as hepatitis A virus and norovirus have traditionally been associated with shellfish consumption, and for this reason, studies have examined the stability of enteric viruses under high pressure. However, kinetic data on enteric virus stability under pressure is needed by processors to better understand the response of viruses throughout the entire treatment time. The kinetic data obtained in this study may be useful for processors wishing to alter high pressure processing conditions to ensure a high quality product in terms of organoleptic and microbiological properties.     

Survival and activity of selected probiotic organisms in set-type yoghurt during cold storage

The growth and metabolism of two probiotic organisms (L. acidophilus LAFTI^® L10 and Lactobacillus casei LAFTI^® L26) and a regular yoghurt culture (L. delbrueckii ssp. bulgaricus Lb1466 and Streptococcus thermophilus St1342) were studied in yoghurt containing 0.5%, 1.0%, and 1.5% (w/v) of high amylose corn starch powder (Hi-maize^®) or inulin. Viable cell counts of probiotic organisms, their metabolites and proteolytic activities, and viscosity of the yoghurts were determined during refrigerated storage for 28 d at 4 ^oC. In the presence of inulin, cultures showed better retention of viability (8.0 log cfu g⁻¹) in comparison with that of Hi-maize, which had a reduction by one log cycle. Lower concentrations of 0.5–1.0% Hi-maize improved (P<0.05) the production of propionic acid and also increased proteolytic activity of probiotic organisms substantially. A greater release of free amino acids may have sustained better growth of the organisms in yoghurts. Supplementation with either Hi-maize or inulin increased the viscosity of probiotic yoghurts significantly (P<0.05).     

Effects of high hydrostatic pressure on physicochemical properties,enzymes activity,and antioxidant capacities of anthocyanins extracts of wild Lonicera caerulea berry

Wild Lonicera caerulea berries were subjected to five different high hydrostatic pressure (HHP) treatments (which resemble the conditions of active component extraction and commercial sterilization). The content of anthocyanins and total phenolics increased by 6.84% and 14.35% (p < 0.05), respectively after treatment at 200 MPa for 5 and 10 min. As HHP increased, a higher loss of active component was observed. The total phenolic contents did not differ significantly between the control and the 400 MPa/20 min treated group (p > 0.05); HHP processing demonstrated better sterilization effect but severely destroyed enzymes. Polyphenol oxidase (PPO) and peroxidase (POD) activity were activated at lower HHP, such as 200 MPa, and decreased at 400–600 MPa. Superoxide dismutase (SOD) maintained good stability under HHP processing. The antioxidant capacities of anthocyanins extracts of wild L. caerulea berry were evaluated by 3 different methods (DPPH assay, oxygen radical absorbance capacity assay, and cellular antioxidant activity assay).Industrial RelevanceFactors such as color, luster, and nutrition often affect consumer choice in food. However, the color and nutrition of foods tend to be destroyed during processing and storage. The demand for healthier and more nutritious food while retaining the color and flavor after processing highlights the need to develop novel and gentler technologies for fruit processing. Recently, high hydrostatic pressure (HHP) technologies have been used in different branches of the food industry. In the present study, the content of active component in blue honeysuckle fruit pulps such as anthocyanins and polyphenols showed tendency to increase and then decrease with increasing pressure at room temperature. Five different HHP treatment groups (resembling the conditions of active component extraction conditions and commercial sterilization) were compared to the control (fresh fruit) and heat-treated group to determine the effects of HHP processing on L. caerulea berry pulps. The aim of this study was to investigate the changes in active component particularly the content and composition of anthocyanins under different high-pressure treatment at room temperature; the color and physicochemical indexes were also analyzed at the same conditions. Low HHP for a long period of time (400 MPa/20 min) demonstrated better results than that with high HHP for a short time (600 MPa/10 min), as indicated by the higher contents of anthocyanins and phenols and stronger antioxidant capacities. Therefore, Low HHP conditions can be used as an auxiliary means of active component extraction. The conditions of HHP processing at low HHP for a long period of time (400 MPa/20 min) can be altered to retain active components during food processing.     

Effect of high pressure (HP) on the quality and shelf life of red mullet (Mullus surmelutus)

The effect of different temperature/time/pressure high hydrostatic pressure (HP) treatment on the quality and shelf life of red mullet were studied. Different high pressure treatments (at 3, 7, 15 and 25 °C, 5 to 10 min and 220, 250 and 330 MPa) were tested to establish the best processing conditions for the quality of red mullet. The effect of the process on the quality of the sample was examined by colour, Trimethylamine nitrogen (TMA-N) and Thiobarbituric acid number (TBA) analysis. Based on the results of the parameters, the best combinations of HP treatments were determined as 220 MPa/5 min/25 °C and 330 MPa/5 min/3 °C for red mullet. The effects of this combination treatment on sensory, chemical and microbiological properties of red mullet stored at 4 °C were studied. The results obtained from this study showed that the shelf life of untreated and HP treated stored at 4 °C, as determined by overall acceptability of sensory and microbiological data, are 12 days for untreated red mullet and 14 days for treated red mullet at 220 MPa for 5 min at 25 °C and 15 days for treated red mullet at 330 MPa for 5 min at 3 °C.Industrial relevanceFresh fish have short shelf life. HP treatment has shown to be an effective method to control pathogen and spoilage microorganisms in fish and fish products. However, high pressure treatment can promote colour and oxidation changes that could modify their sensory characteristics. The main objective of the first part of this study was to detect the best combination among the applied pressure (220, 250 and 330 MPa), temperature (3, 7, 15 and 25 °C) and time (5 and 10 min) combinations. The treatment ranges were chosen according to the unchanging colour, lower TBA value and TMA stability by HP and considering the economical aspects of HP processing. In the second part of the study, HP was applied on the selected samples and a shelf-life study was performed by measuring the changes in the quality parameters, of the samples throughout their storage. The storage conditions were set so as to achieve refrigeration handling (4 °C). Shelf-life estimation was performed according to the data obtained. HP (at 220 MPa for 5 min at 25 °C and at 330 MPa for 5 min at 3 °C) treatment is the most effective treatment for shelf-life extension as compared to non-treated red mullet.     

Physical characteristics of set yoghurt made with altered casein to whey protein ratios and EPS-producing starter cultures at 9 and 14% total solids

This study investigated firmness and syneresis of set yoghurts made at the CN to WP ratios of 4:1, 3:1, 2:1 and 1:1 using non-EPS-, capsular EPS- and ropy EPS-producing starter cultures. The yoghurts were made at 9 and 14% (w/w) total solids. The total solids, total protein, the concentration of lactose and the ratios of CN to WP as well as the protein's profiles (native- polyacrylamide gel electrophoresis) in heated and unheated milk blends were investigated. The level of soluble denatured whey protein aggregates in heated milk was also determined. The concentration of EPS, firmness and level of spontaneous syneresis in set yoghurt were monitored weekly throughout 28 days of storage. The microstructure of the set yoghurt made with milk blends at the CN to WP ratio of 4:1 and using three types of starter cultures was carried out after 1 day of storage. There was no difference in the total solids, total protein and lactose concentration of liquid milk blends, except the CN to WP ratios. There was no difference in whey protein denaturation between milk blends. The level of soluble denatured whey protein aggregates in heated milk blends decreased with reducing CN to WP ratio. The firmness and the level of spontaneous syneresis in set yoghurts decreased as the CN to WP ratios were reduced. The use of EPS-producing starter cultures reduced firmness and syneresis and changed the protein matrix in the microstructure of set yoghurts made at 9% (w/w) total solids compared to the control products. These were not observed in set yoghurts made at 14% (w/w) total solids.     

Impact of processing on stability of angiotensin I-converting enzyme (ACE) inhibitory peptides obtained from tuna cooking juice

In this study, angiotensin I-converting enzyme (ACE) inhibitory peptides, which had previously been identified in an active gelfiltration fraction from tuna cooking juice, were examined for the stability of their inhibitory properties and composition changes during processing and in the presence of gastrointestinal proteases. Results indicated that ACE inhibitory peptides reserved almost the same composition before and after various temperatures (20–100 °C), levels of pressure (50–300 MPa) and pH (2–10) treatments. ACE inhibitory peptides retained 95–99% activity after simulated digestion. High Performance Liquid Chromatography (HPLC) chromatograph peptide mappings exhibited slight differences before and after temperature (100 °C), pressure (300 MPa) and pH (2, 10) treatments. Our results indicate that tuna cooking juice-derived ACE inhibitory peptides possess some degree resistance to the influence of temperature, pressure, pH treatments, and gastrointestinal proteases.