Caffeine metabolism rate influences coffee perception,preferences and intake

Several factors – genetic, demographic and environmental – contribute to individual differences in sensitivity to the pharmacological effects of caffeine. Caffeine metabolism influences coffee consumption, but its effect on bitterness perception in, and preference for, coffee is unknown.This study explores the possible relationship between caffeine metabolism rate and coffee preferences and consumption habits. In addition, the extent to which caffeine metabolism interacted with variations in bitterness perception was investigated. Caffeine metabolism rate was assayed by competitive immuno-enzymatic assay in one-hundred thirty-five coffee consumers who provided saliva samples after 12 h caffeine abstinence and at 30 and 90 min after ingestion of caffeine (100 mg). A caffeine metabolism index (CmI) was computed as the ratio between the amount of residual caffeine in saliva 60 min after the adsorption peak and the amount of caffeine at the adsorption peak corrected with the baseline. Ninety-one subjects were selected to investigate the relationships between inter-individual variation in caffeine metabolism, bitterness perception and coffee preference. Subjects rated liking for, and sourness, bitterness and astringency of, six unsweetened and freely sweetened coffee samples varying in roasting degree, caffeine content and bitterness. They also rated the bitterness of six caffeine and six quinine (equi-intense) solutions. Finally, subjects choose coffee to drink on the basis of a label (strong vs balanced flavor) both after caffeine abstinence and after no restrictions on caffeine intake. The CmI was strongly associated with the frequency of daily coffee consumption. Subjects with lower CmI gave higher bitterness ratings than other subjects for both coffee and caffeine solutions, but not for quinine solutions. They also added more sugar to the coffee samples. Following caffeine abstinence, all subjects chose the “strong flavor” coffee, while without caffeine restrictions, subjects with lower CmI preferentially tended to choose the “balanced flavor” coffee. These results provide the first link between caffeine metabolism and bitterness perception, and to the use of sugar to modify coffee bitterness.     

The effect of inhomogeneous quinine and hydrocolloid distributions on the bitterness of model gels

This study investigated the effect of inhomogeneous distributions of quinine on bitterness intensity of gelatine–agar composite gels. It also investigated the effect of inhomogeneous distributions of the gel’s hydrocolloid constituents (the gelatine and agar) on the bitterness intensity of the quinine. Fifty-two screened subjects participated in four paired comparison tests comparing inhomogeneous designs of quinine (with a homogeneous hydrocolloid distribution) and inhomogeneous designs of the hydrocolloids (with a homogeneous quinine distribution), against a homogeneous control of identical overall quinine and hydrocolloid composition. Using the same gel designs, a mastication trial was undertaken where ten subjects were asked to chew each gel system until the point of swallowing, and eleven subjects participated in a time-intensity trial where bitterness intensity was monitored during mastication and after expectoration. Paired comparison tests showed that the inhomogeneous distribution of quinine increased bitterness intensity, while inhomogeneous distributions of the hydrocolloids did not. Mastication was not influenced by changes in the distribution of quinine or the hydrocolloids. Time intensity curves showed the gels having an inhomogeneous distribution of quinine had greater bitterness intensity throughout mastication, however no differences in bitterness intensity were observed between any gel designs in the latter stages of aftertaste measurements. Time intensity curves also showed a slight delay in time to maximum bitterness intensity for the gels with inhomogeneous distributions of hydrocolloids. Results suggest a homogeneous distribution of bitter compounds is the most suitable structure for minimising bitterness perception.     

Sensory profile,acceptability, and their relationship for diabetic/reduced calorie chocolates

The purpose of this study was to determine the sensory properties and acceptability of lab developed prototypes of conventional, diabetic (with no sugar), and diabetic/reduced calorie milk chocolates (no sugar and 25% calorie reduction) with high-intensity sweeteners, sucralose and stevioside, and partial fat replacement with whey protein concentrate (WPC). PLS was performed in order to relate sensory properties and consumer acceptability and to determine drivers of liking and disliking. There was no difference between conventional, diabetic and diabetic/reduced calorie milk chocolates for brightness, cocoa aroma, cocoa butter aroma, and cocoa flavor (p > 0.05). Acceptability was higher for sucrose substitution by sucralose than by stevioside and partial fat replacement reduced acceptability of flavor even more (p ? 0.05). Crucial attributes which determine consumer acceptability in samples are sweet aroma, melting rate, and sweetness, whereas bitterness, bitter aftertaste, adherence, and sandiness were drivers of disliking.     

Alternatives to reduce the bitterness,astringency and characteristic flavour of antioxidant extracts

There is increasing interest in the development and use of polyphenolic-rich antioxidant extracts as functional ingredients. However, their bitterness, astringency and characteristic flavour could limit their incorporation in foods and beverages. Four alternatives to reduce the bitterness, astringency, and characteristic flavour of antioxidant extracts of two Uruguayan native plants (Achyrocline satureioides and Baccharis trimera) were studied: sucrose, sucralose, polydextrose, and milk. All the evaluated alternatives highly significantly (p < 0.001) reduced the bitterness, astringency and characteristic flavour of the extracts. However, their effectiveness depended on the type and concentration of the antioxidant extract being considered. Milk was the most effective inhibitor of the bitterness, astringency and characteristic flavour of A. satureioides extracts; whereas when extracts from B. trimera were considered, sucrose was the most effective alternative. Results from the present work suggest that sweetened dairy products could be interesting carriers for the development of functional foods containing polyphenolic-rich antioxidant extracts.     

Effect of preheating temperature and calcium ions on the properties of cold-set soybean protein gel

To elucidate the effect of preheating temperature and calcium ions on the properties of cold-set soybean protein gel, Ca²⁺ induced gelation of soybean protein were investigated by rheological approaches, electrophoresis analysis, confocal scanning laser microscopy (CSLM) and surface hydrophobicity (S₀). The results showed that, both CaCl₂ concentration (20–40 mM) and preheating temperature (80–120 °C) took significant influence on the dynamic viscoelasticity of the gel samples. The bands distribution of samples preheated at 120 °C were different from the bands distribution of samples preheated below 100 °C in denature and native electrophoresis. The CSLM analysis showed that the gel became coarser as the Ca²⁺ increased. On the other hand, two different kinds of gel were shown under the same Ca²⁺ concentration: a bead-like structure (below 100 °C) and a filamentous structure (above 100 °C). According to fractal theory, weak-linked gel (α was >0.8) was formed when preheating below 100 °C, while a transition gel (α = 0.52–0.62) was obtained when preheating over 100 °C. All these results suggested that the preheating temperature influence the type of cold-set gel.     

Consumption of lingonberries by TAS2R38 genotype and sensory quality of texture-designed lingonberry samples

Bitter taste receptor genotypes may be associated with the perception of bitterness in berries, and different processing methods may be used to modify the flavor of berry products. The aims of the present study were to investigate the consumption frequency of lingonberries among TAS2R38 genotyped subjects (n = 83) and to evaluate the sensory characteristics of different texture-modified lingonberry samples (subjects n = 12, samples n = 8). Reported intake of lingonberries varied with TAS2R38 genotype, with more bitter sensitive individuals consuming them less frequently. The flavor profile of lingonberries was modifiable by food structure. In particular, foam and/or emulsion structures decreased the perceived intensity of bitterness, astringency and sourness of lingonberry samples. Sweetness was significantly higher in heavy foamed jelly and foamed emulsion compared to pulp or foamed juice. In conclusion, new flavor and texture modification options should be investigated to increase the palatability and consumption of bitter tasting foods.     

Ability of conventional and nutritionally-modified whey protein concentrates to stabilize oil-in-water emulsions

The ability of a modified whey protein concentrate (MWPC), which contains relatively high proportions of phospholipid and high molecular weight protein fractions, to form and stabilize 10 wt% corn oil-in-water emulsions (pH 7.0, 5 mM phosphate buffer) was compared with that of a conventional whey protein concentrate (CWPC). The MWPC stabilized emulsions required less protein to prepare stable emulsions with monomodal particle size distributions and small mean droplet diameters (d₄₃ ≈ 0.3 μm at [WPC] ⩾ 0.5 wt%) than CWPC stabilized emulsions (d₄₃ ≈ 0.4 μm at [WPC] ⩾ 0.9 wt%) under similar homogenization conditions (5 passes at 5000 psi). In addition, the emulsions stabilized by 0.9 wt% MWPC were more stable to high salt concentration (NaCl ⩽ 200 mM), thermal processing (30–90 °C for 30 min) and pH (3, 6 and 7) than those stabilized by the same concentration of CWPC, which was attributed to polymeric steric repulsion rather than electrostatic repulsion. This study has important implications for the wide application of WPC as a natural emulsifier in food products.     

Genetic and environmental influences on liking and reported intakes of vegetables in Irish children

Variation in the bitterness of 6-n-propylthiouracil (PROP) is partially explained by polymorphisms in the TAS2R38 gene. Based on their perception of bitterness from PROP, people may be classified into non-, medium and supertasters. PROP perception has previously been linked to liking for cruciferous vegetables in children in some studies, but only one study to date has examined TAS2R38 genotype and its relationship with vegetable intake in children. Children’s vegetable consumption generally does not meet the recommended guidelines, thus the present study aimed to examine the influence of oral sensory measures, genetic variation and social factors on vegetable liking and intake. Vegetable liking in 7–13 year old Irish children (n = 525) was measured on a 5-point liking scale, and dietary intakes were assessed via a 3-day diet history. Vegetable intakes were calculated and standardised per kg body weight. A subset of children (n = 485) were genotyped for SNPs in TAS2R38, (A49P, V262A, I296V), and fungiform papilla (FP) were counted. The bitterness of PROP and sweetness of sucrose were rated on a generalised labelled magnitude scale (gLMS). PROP and sucrose intensity were significantly correlated (R² = 0.33, p = 0.001), although neither sucrose intensity nor FP density differed across the TAS2R38 genotype groups. Supertasters were less likely than nontasters to have tried/tasted cruciferous vegetables p < 0.04). A small, positive correlation was seen in FP density and vegetable intake, but only in the AVI homozygous children, (R² = 0.17, p = 0.035). 174 Nutrient acceptable children reported an intake of one or more of the vegetables of interest in the 3-day period. Liking of cruciferous vegetables and reported intake were significantly correlated. In multiple regression analyses in this subsection of the cohort, socioeconomic status (SES) and gender were more important than PROP bitterness or TAS2R38 genotype in predicting intakes (approximately 15% of liking and 67% of intake was explained by these models). Overall, neither PROP taster status nor TAS2R38 genotype alone had significant impact on bitter vegetable liking or intake. Further research into FP density and vegetable liking and intake may be warranted.     

Taste intensities of ten vegetables commonly consumed in the Netherlands

Bitterness has been suggested to be the main reason for the limited palatability of several vegetables. Vegetable acceptance has been associated with preparation method. However, the taste intensity of a variety of vegetables prepared by different methods has not been studied yet. The objective of this study is to assess the intensity of the five basic tastes and fattiness of ten vegetables commonly consumed in the Netherlands prepared by different methods using the modified Spectrum method. Intensities of sweetness, sourness, bitterness, umami, saltiness and fattiness were assessed for ten vegetables (cauliflower, broccoli, leek, carrot, onion, red bell pepper, French beans, tomato, cucumber and iceberg lettuce) by a panel (n = 9) trained in a modified Spectrum method. Each vegetable was assessed prepared by different methods (raw, cooked, mashed and as a cold pressed juice). Spectrum based reference solutions were available with fixed reference points at 13.3 mm (R1), 33.3 mm (R2) and 66.7 mm (R3) for each taste modality on a 100 mm line scale. For saltiness, R1 and R3 differed (16.7 mm and 56.7 mm). Mean intensities of all taste modalities and fattiness for all vegetables were mostly below R1 (13.3 mm). Significant differences (p < 0.05) within vegetables between preparation methods were found. Sweetness was the most intensive taste, followed by sourness, bitterness, fattiness, umami and saltiness. In conclusion, all ten vegetables prepared by different methods showed low mean intensities of all taste modalities and fattiness. Preparation method affected taste and fattiness intensity and the effect differed by vegetable type.     

Vanillin inhibits pathogenic and spoilage microorganisms in vitro and aerobic microbial growth in fresh-cut apples

The antimicrobial effect of vanillin against four pathogenic or indicator organisms; Escherichia coli, Pseudomonas aeruginosa, Enterobacter aerogenes, and Salmonella enterica subsp. enterica serovar Newport and four spoilage organisms; Candida albicans, Lactobacillus casei, Penicillum expansum, and Saccharomyces cerevisiae that could be associated with contaminated fresh-cut produce, was examined. The minimal inhibitory concentration (MIC) of vanillin was dependent upon the microorganism and this ranged between 6 and 18 mM. When incorporated with a commercial anti-browning dipping solution (calcium ascorbate, NatureSeal™), 12 mM vanillin inhibited the total aerobic microbial growth by 37% and 66% in fresh-cut ‘Empire’ and ‘Crispin’ apples, respectively, during storage at 4 °C for 19 days. Vanillin (12 mM) did not influence the control of enzymatic browning and softening by NatureSeal. These results provide a new insight for vanillin as a potential antimicrobial agent for refrigerated fresh-cut fruits and vegetables.     

Effect of processing conditions on the structure of monostearin–oil–water gels

The effect of processing conditions on the formation and stability of a gel comprised of oil, water, monostearin and stearic acid was studied. Processing conditions (homogenization rate (10,000–30,000 rpm), cooling rate (0.05–20 °C/min), homogenization temperature (70–95 °C)) had no effect on the initial storage modulus and melting temperature of the gel. Salt (NaCl) addition to the aqueous phase in the range 0–0.25% did not affect these parameters either; however, 0.5% salt addition lead to a ∼2 °C decrease in melting temperature and a doubling of the storage modulus. Optimal preparation conditions for the gel were mainly determined from its microstructure by polarized light microscopy – a smaller globule size and a more homogenous size distribution were considered a desirable feature. Optimum conditions included homogenization rates greater than 20,000 rpm, cooling rates above 6 °C/min, homogenization temperatures above, but close to, the Krafft temperature of monostearin (72 °C), and 0% salt concentration. The gelation temperature decreased by 2 °C with each 1 °C/min increase in cooling rate, from 1 °C/min to 5 °C/min.     

Sensory changes during bottle storage of Spanish red wines under different initial oxygen doses

Sixteen commercial Spanish red wines selected to cover a wide range of sensory properties were stored at 25 °C for 6 months in air-tight containers under different oxygen doses (0–30 mg L^− 1) mimicking real and extreme bottling situations. The 16 initial samples (before storage) and the 80 stored samples (16 wines × 5 oxygen doses) were submitted to sensory analysis. Sensory changes related to post-bottling storage and initial oxygen dose were evaluated by means of discriminant and characterisation sensory strategies.Significant increases in black fruits, dried fruits, woody, lactic and stronger increases in cooked vegetables and spicy notes reveal a general pattern of aroma evolution. Remarkable departures to this general pattern have been observed, which can be related to the initial sensory properties of the wines and to their basic polyphenolic composition. The effect of post-bottling storage in bitterness is wine dependent, while global decreases in both global intensity and persistence evaluated in mouth are observed. Discrete increases in astringency are observed for wines with the lowest initial astringent scores. Important sensory interactions between aroma attributes (herbal and spicy) and bitterness and between roasted and astringency perception are shown. Little impact of the initial oxygen dose in the in-mouth sensory properties is reported. These results are relevant for wine experts in that they help understanding the evolution of wine sensory properties in the bottling stage. This study may help them to develop strategies for managing this winemaking stage with objective criteria.     

Texture and structure of pressure-shift-frozen agar gel with high visco-elasticity

To determine the effects of sucrose and high-pressure-freezing, two kinds of agar gel were compared; A gel with high visco-elasticity and B gel, an ordinary dessert gel. Both agar gels with 0, 5, 10 or 20% sucrose were frozen at 0.1–686 MPa and −20 °C. They were frozen during pressurization, and exothermic peaks were detected at 0.1, 100, 600 and 686 MPa and −20 °C (freezing). However, at 200 MPa, they did not freeze but froze with released pressure (pressure-shift-freezing). Thus, the amount of syneresis from gel pressure-shift-frozen at 200 MPa was smaller than that from gel frozen at other pressures. Also, amount of syneresis from A was smaller than B. In addition, compared to control gels, the appearance of 0% sucrose–agar gels frozen at 0.1, 100, 600 and 686 MPa differed greatly due to syneresis and a volumetric shrinkage of the gel. It was apparent that the rupture stress of the gels decreased, strain and size of ice crystals increased and quality declined. Conversely, due to quick freezing, the texture and structure of both A and B pressure-shift-frozen at 200 MPa were better than the other pressure-treated gels and gels frozen in freezers (−20, −30 or −80 °C) at atmospheric pressure. Consequently, pressure-shift-freezing was more effective. However, texture, structure and syneresis of A were somewhat better than that of B. It was found that the addition of sucrose to the gel was effective in improving the quality of frozen agar gels.     

Modification of perceived beer bitterness intensity,character and temporal profile by hop aroma extract

The effect of hop aroma on perceived bitterness intensity, character and temporal profile of beer was investigated. A hop aroma extract was added at 3 levels (0, 245, 490 mg/L) to beers at low, medium and high bitterness. Beers were evaluated for perceived bitterness intensity, harshness, roundedness and linger by a trained panel using a rank-rating technique at each bitterness level, with and without nose clips. The use of nose clips enabled the olfactory aspect to be decoupled from taste and mouthfeel aspects of bitterness perception. Results showed significant modification of perceived bitterness in beer by hop aroma depending on the inherent level of bitterness. These modifications were mainly driven by olfaction – in an example of taste-aroma interactions, as well as certain tactile sensations elicited by the hop aroma extract in the oral cavity. At low bitterness, beers with hop aroma added were perceived as more bitter, and of ‘rounded’ bitterness character relative to those without hop aroma. When judges used nose clips, this effect was completely eliminated but the sample was perceived to have a ‘harsh’ bitterness character. Conversely, at high bitterness, even when nose clips were used, judges still perceived beers containing hop aroma to be more bitter. These increases in bitterness perception with nose clips indicates the stimulating of other receptors, e.g. trigeminal receptors by hop aroma extract, which in tandem with the high bitterness, cause perceptual interactions enhancing bitterness intensity and also affecting bitterness character. Bitterness character attributes such as ‘round’ and ‘harsh’ were found to significantly depend on bitterness and aroma levels, with the second level of aroma addition (245 mg/L) giving a ‘rounded’ bitterness in low bitterness beers but ‘harsh’ bitterness in high bitterness beers. The impact of aroma on temporal bitterness was also confirmed with time-intensity measurements, and found to be mostly significant at the highest level of hop aroma addition (490 mg/L) in low bitterness beers. These findings represent a significant step forward in terms of understanding bitterness flavour perception and the wider impact of hop compounds on sensory perception.     

Heat processed whey-protein food emulsions and growth of shear-induced cracks during cooling

When high fat (40 g oil /100 g) food dressings emulsified by whey protein were heat-filled (80°C) into plastic-bottles, large visible cracks developed in the dressings after cooling. The occurrence of cracks was dependent on the length of the heat treatment, pH and protein concentration. Heating (2 h at 80°C), low pH (pH 3) and high protein concentrations (1.5 g/100 g) increased the number of cracks. Dressings with cracks were more viscous and had a broader particle size distribution than dressings devoid of cracks. During heating at 80°C the complex modulus (G¹) measured at low deformation increased sharply, signifying the formation of a three-dimensional network as a result of aggregation of whey protein bridging the fat-droplets. Confocal laser scanning microscopy revealed differences in microstructure dependent on cooling rate and pH. At slow cooling and pH 3 the network structure was inhomogeneous with large voids, while at pH 4, closer to the isoelectrical point, the structure was more compact aggregated and homogeneous. The gels at pH 3 were strain sensitive and seemed more prone to localized fracture. A strong (r=0.86) relationship between a visible quality defect called cracks and the gel properties of the emulsion was found. Avoiding cracks called for a strict control of protein concentration, pH and holding time at higher temperatures.     

Effect of transglutaminase on rheological properties and microstructure of chemically acidified sodium caseinate gels

The mechanical properties and microstructure of 2.7% and 4.5% sodium caseinate gels chemically acidified by glucono-δ-lactone (GDL) and cross-linked by microbial transglutaminase (TG) were studied. The acidification was performed at different temperatures. According to SDS–PAGE TG clearly caused polymerisation of caseinate irrespective of the treatment temperature (4–50 °C), The cross-linking of the proteins was more extensive at temperatures 22–50 °C. Low amplitude viscoelastic measurements showed that 4.5% caseinate gels acidified at 50 °C were formed much faster than gels acidified at 22 °C. TG only slightly increased the time of gelling. Control gels prepared without TG at temperatures of 4, 22, 37 and 50 °C were mechanically weak. Examination of the control gels with a confocal laser scanning microscope showed that gels formed at 37 and 50 °C were coarse and porous with large cavities between particle aggregates, whereas those formed at 22 °C were much more homogeneous. The TG-treated and acidified sodium caseinate dispersions formed firm gels, indicating cross-linking of casein proteins. Interestingly, the strongest gels were formed at 22 and 37 °C. TG treatment improved the homogeneity of the gel structure at temperatures of 37 and 50 °C. The hardness of TG-treated gels acidified at 4 °C increased during 1 week of storage.     

Discussion on the objective evaluation of virgin olive oil bitterness

The study aims at investigating the suitability of absorbance at 225 nm as an objective means to evaluate virgin olive oil (VOO) bitterness. Calculation of oleuropein score (OLS) using a standard curve instead of the so far employed K₂₂₅ value is proposed and a “taste index” based on the total phenol content determined by fluorimetry is examined as a complementary tool. Data from sensory evaluation of a series of VOO samples and RP-HPLC determination of phenolic compounds using diode array, fluorimetric or MS detection supported the applicability and merits of the introduced criteria. Phenol profiling using fluorescence detection (280 nm_excitation/320 nm_emission) became useful regarding oil bitterness. The presence of the non-fluorescent elenolic acid at 225 nm, indicated that the K₂₂₅ value is influenced by the presence of this non-bitter compound found at significant levels even in fresh oils. Our finding offers further ground to our proposal for the calculation of the “taste index”.     

Effect of ozone on microbial,chemical and sensory attributes of shucked mussels

The effect of ozonation in aqueous solution (O₃ concentration=1 mg/l, time of ozonation: 60 and 90 min) on the shelf-life of shucked, vacuum-packaged mussels, stored under refrigeration was studied by monitoring the microbiological, chemical and sensory changes occurring in mussel samples, for a period of 12 days. Non-ozonated vacuum-packaged mussels served as the control sample. Ozonation affected populations of bacteria namely, aerobic plate count (APC) (0.7–2.1 log cycle reduction), Pseudomonas spp. (0.5–1.1 log cycle reduction) and H₂S-producing bacteria (1.1–2.5 log cycle reduction), Brochothrix thermosphacta (0.3–1.4 log cycle reduction), lactic acid bacteria (0.3–0.8 log cycle reduction) and Enterobacteriaceae (0.5–1.5 log cycle reduction). The effect of ozonation was more pronounced at the longer time of ozonation. Of the chemical indicators of spoilage monitored, trimethylamine values of all mussel samples remained relatively low throughout the entire storage period, attaining values of 7.5, 6.0 and 6.4 mg N/100 g for the control and ozonated for 60 and 90 min samples, respectively, on day 12 of storage. Total volatile basic nitrogen (TVB-N) values similarly remained relatively low (⩽20 mg N/100 g) until day 6 of storage, and increased to 31.9, 24.2 and 26.9 mg N/100 g mussel meat for the control and ozonated for 60 and 90 min samples, respectively, on day 12 of storage. Initial TBA values were surprisingly high (30–35 mg MA/kg) and decreased to 23.0, 21.7 and 13.3 mg MA/kg mussel meat on day 12 of storage for the control and the ozonated for 60 and 90 min samples, respectively. Sensory evaluation (odor, taste and texture) of cooked mussels showed a good correlation with bacterial populations. On the basis of sensory analyses, a shelf-life of 12 days was obtained for vacuum-packaged mussels ozonated for 90 min as compared to a shelf-life of 9 days for the control sample.     

Proteolysis and storage stability of UHT milk produced in Turkey

The effect of raw milk quality (total and psychrotrophic bacterial and somatic cell counts, proteinase and plasmin activity) and UHT temperature (145 or 150 °C for 4 s) on proteolysis in UHT milk processed by a direct (steam-injection) system was investigated during storage at 25 °C for 180 d. High proteinase activity was measured in low-quality raw milk, which had high somatic cell count, bacterial count and plasmin activity. The levels of 12% trichloroacetic acid–soluble and pH 4.6-soluble nitrogen in all milk samples increased during storage, and samples produced from low-quality milk at the lower UHT temperature (145 °C) showed the highest values. Bitterness in UHT milk processed from low-quality milk at 145 °C increased during storage; gelation occurred in that milk after 150 d. The RP-HPLC profiles of pH 4.6-soluble fraction of the UHT milk samples produced at 150 °C showed quite small number of peaks after 180 d of storage. Sterilization at 150 °C extended the shelf-life of the UHT milk by reducing proteolysis, gelation and bitterness.     

Comparison of properties of oil-in-water emulsions stabilized by coconut cream proteins with those stabilized by whey protein isolate

Coconut cream protein (CCP) fractions were isolated from coconuts using two different isolation procedures: isoelectric precipitation (CCP1-fraction) and freeze–thaw treatment (CCP2-fraction). The ability of these protein fractions to form and stabilize oil-in-water emulsions was compared with that of whey protein isolate (WPI). Protein solubility was a minimum at ∼pH 4, 4.5 and 5 for CCP1, CCP2, and WPI, respectively, and decreased with increasing salt concentration (0–200 mM NaCl) for the coconut proteins. All of the proteins studied were surface active, but WPI was more surface active than the two coconut cream proteins. The two coconut cream proteins were used to prepare 10 wt% corn oil-in-water emulsions (pH 6.2, 5 mM phosphate buffer). CCP2 emulsions had smaller mean droplet diameters (d₃₂ ≈ 2 μm) than CCP1 emulsions (d₃₂ ≈ 5 μm). Corn oil-in-water emulsions (10 wt%) stabilized by 0.2 wt% CCP2 and WPI were prepared with different pH values (3–8), salt concentrations (0–500 mM NaCl) and thermal treatments (50–90 °C for 30 min). Considerable droplet flocculation occurred in the emulsions near the isoelectric point of the proteins: CCP2 (pH ∼ 4.3); WPI (pH ∼ 4.8). Emulsions with monomodal particle size distributions, small mean droplet diameters, and good creaming stability could be produced at pH 7 for WPI, but CCP2 produced bimodal distributions at this pH. The CCP2 and WPI emulsions remained relatively stable to droplet aggregation and creaming at NaCl concentrations ⩽50 and ⩽100 mM, respectively. In the absence of salt, both CCP2 and WPI emulsions were quite stable to thermal treatments (50–90 °C for 30 min).