Physicochemical and sensory properties of kefir containing inulin and oligofructose

This study concerns the physicochemical and sensory analysis of stirred kefirs made at a laboratory scale, in which one‐third of the skim milk powder (SMP) was replaced by different inulins (long chain, native and oligofructose). The reference kefirs contained 12 g/100 g of SMP or whole milk powder. Rheological analysis showed that the kefirs were viscoelastic materials with thixotropic and shear‐thinning behaviour. Rheological data showed that SMP can be successfully substituted by long‐chain inulin; however, sensory evaluation indicated that substitution of SMP by any other kinds of inulin significantly decreased the consistency of kefirs while not affecting their flavour and odour.     

Investigation of the potential for using inulin HPX as a fat replacer in yoghurt production

In this study yoghurts produced from full-fat milk (3.2%) and from low-fat milk (0.5%), with 0.7% and 2.7% added inulin, were compared. Inulin addition did not influence bacterial counts and acidity. Yoghurt from full-fat milk showed the highest values of apparent viscosity, followed by yoghurt with 2.7% of inulin. The sensory properties of the yoghurts differed mainly in terms of texture and taste. The highest scores were gained by yoghurt from full-fat milk, but yoghurt with 2.7% of inulin received only slightly lower scores. The results indicate that inulin has potential as a fat replacer in yoghurt.     

Effects of poly‐γ‐glutamic acid on the physicochemical characteristics of skim milk yoghurt

The physicochemical and sensory properties of skim milk yoghurts containing poly‐γ‐glutamic acid (PGA) at different levels (0.0025, 0.005 and 0.01%) were evaluated. Addition of PGA up to 0.01% to reconstituted skim milk (11%, w/v) did not affect the growth of lactic acid bacteria or the development of titratable acidity in yoghurt, whereas full‐fat control yoghurt had reduced acid production. No changes were found in viable cell counts of PGA yoghurts during storage (4 weeks at 4 °C). The addition of PGA (0.005%) significantly decreased syneresis in skim milk yoghurt and did not cause any undesirable effects in sensory acceptability.     

Carbohydrate-based fat replacers in the modification of the rheological, textural and sensory quality of yoghurt: comparative study of the utilisation of barley beta-glucan, guar gum and inulin

Barley beta‐glucan, partially hydrolysed guar gum and inulin were used in the processing of low‐fat yoghurts. The possible beneficial effects of carbohydrate fat replacers on the rheological, textural and sensory quality of low‐fat yoghurt‐based products were determined. Comparisons were made between the sample yoghurts made from a low‐fat milk base, and full‐fat and low‐fat yoghurt controls. The inclusion of the carbohydrate components reduced product syneresis and improved the texture and rheological properties of the low‐fat‐based products so that their quality characteristics were similar to yoghurt made with full‐fat milk. Both the type and also the amount of carbohydrate component altered product characteristics. Beta‐glucan addition at low level (0.5%) was effective in improving serum retention of the yoghurt and its viscoelastic nature (G′, G′ and tan δ). In contrast, higher levels (above 2%) of inulin and guar gum were needed to exert significant improvements in the textural characteristics of yoghurt. Sensory analysis conducted on the samples illustrated that the inclusion of carbohydrate‐based fat replacers could be successfully utilised to mimic full‐fat products.     

Effect of microfluidization of heat-treated milk on rheology and sensory properties of reduced fat yoghurt

The effects of microfluidization at 150 MPa (MFz) and conventional homogenization at 20/5 MPa (CH) of heat-treated milk on the rheology and sensory properties of non- (0.1%) and low- (1.5%) fat stirred yoghurts were compared. Homogenization conditions clearly affected the sensory properties of reduced-fat yoghurts, but the effect was highly dependent on fat content. MFz of heat-treated milk yielded products with very different sensory profiles from the conventional yoghurts. For non-fat yoghurts, MFz of heat-treated milk enhanced the perception of buttermilk and soft cheese flavours, and natural yoghurt aroma and flavour, but also increased the intensity of undesirable mouthfeel characteristics such as chalkiness, mouth-dryness and astringency. For low-fat yoghurts, MFz significantly improved creaminess and desirable texture characteristics such as smoothness, cohesiveness, thickness, and oral and spoon viscosity. These differences in sensory profiles, especially textural properties, were partially related to rheological properties, particularly flow behaviour. MFz of heat-treated milk resulted in non- and low-fat yoghurts with higher yield stress, more pronounced hysteresis effect and higher viscosity than those of CH yoghurts of similar fat contents. These findings suggest that microfluidization may have applications for production of high-quality yoghurt with reduced-fat content.     

N-Glycosidase F improves gel firmness in fermented milk products

Healthier dairy products can be obtained by reducing fat content, but removal of fat from fermented milk products causes a reduction in gel firmness. To compensate, costly protein enrichment with either skim milk powder or whey protein concentrate is typically necessary. An attractive solution could be substitution of protein enrichment with a texturising enzyme. We aimed to identify such enzymes and found that after treatment with N-glycosidase-F (PNGase-F), yoghurt gel firmness increased. Highly pure PNGase-F was produced in Escherichia coli and our studies revealed that PNGase-F could substitute addition of 2% SMP used for protein enrichment in yoghurt. The effect on gel firmness of PNGase-F was stable over a period of 28 days and a sensory panel described the yoghurts as having improved thickness. Our study shows that it is indeed possible to find satisfying enzyme solutions that can replace the need for protein enrichment.     

Effect of long‐chain inulin on the texture profile and survival of Lactobacillus paracasei ssp. paracasei in set yoghurts during refrigerated storage

The effects of adding inulin at 20 g/L as a fat replacer and probiotic bacteria on the physicochemical and textural characteristics of yoghurt were studied. The ability of long‐chain inulin to improve the probiotic (Lactobacillus paracasei ssp. paracasei) bacteria viability in yoghurt was investigated. The addition of inulin made the texture (firmness, cohesiveness, adhesiveness and gumminess) of skimmed yoghurt similar to that of whole yoghurt, demonstrating the role of inulin as a fat replacer. However inulin increased syneresis and did not influence the viability of probiotic bacteria in the yoghurts. The addition of probiotic bacteria in yoghurts improved syneresis and increased firmness and gumminess.     

Rheological,texture and sensory properties of kefir with high performance and native inulin

Rheological, textural, and sensory properties of kefirs with inulin were analysed. Besides, the effect of skim milk powder (SMP) and milk fat substitution was examined by high performance (HP) and native inulin. One-third of SMP was substituted by native (IQ) or HP (TEX!, HPX) inulin. Hardness of kefir with IQ inulin was lower than that with HP inulins or pure SMP. Analysis of cohesiveness and adhesiveness showed that kefir with inulin had higher firmness. Rheological analysis revealed that all manufactured kefirs had higher storage than loss modulus, and exhibited thixotropic and shear thinning behaviour. There were no significant differences in odour and consistency between kefirs with and without inulin. Only in case of whole milk powder (WMP) kefir, panellists noticed the difference in flavour, although kefirs based on SMP had the same scores. Substitution of SMP by inulin allowed for reducing 15% and 37% of caloric value in comparison with SMP and WMP kefir, respectively.     

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.     

Comparison of the effects of high-pressure microfluidization and conventional homogenization of milk on particle size,water retention and texture of non-fat and low-fat yoghurts

The effect of high-pressure homogenization using a Microfluidizer^® on texture, water-holding capacity, and extent of syneresis on stirred yoghurts was compared with that of conventional homogenization. The effect of homogenization condition on particle size was also assessed in milk and in yoghurt. Stirred yoghurts were prepared from recombined milk samples (0 and 1.5% fat) heat-treated (95 °C, 2 min) and then treated by conventional valve homogenization at 25 MPa or microfluidization at 150 MPa. Homogenization conditions influenced the particle size in milk, gel particle size, and textural quality of stirred yoghurts in a manner dependent upon fat content. Milk microfluidized at 150 MPa had smaller particle size than homogenized milk, but resulted in larger particles in yoghurt. Microfluidization of low-fat milk modified the microstructure of yoghurt, giving more interconnectivity in the protein networks with embedded fat globules, but with similar texture profiles and water retention compared with yoghurt made from conventionally homogenized milk.     

The effect of hydrolysed tragacanth gum and inulin on the probiotic viability and quality characteristics of low‐fat yoghurt

This study investigates the effect of supplementation of tragacanth gum (GT, 0.05% w/v), low molecular weight gum tragacanth (LMWGT, 0.5% w/v) and inulin (0.5% w/v) on the viability of Bifidobacterium bifidum and the quality parameters of low‐fat yoghurt during a three‐week storage period. The count of probiotics was found to be 7.8 log cfu/g in inulin, and LMWGT enriched yoghurts at the end of the storage period. The minimum water holding capacity and the maximum syneresis values were also obtained in the low‐fat yoghurt enriched with GT throughout the storage time. The samples containing inulin and LMWGT revealed sensory attributes that were judged superior compared to those in GT.     

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.     

Acidification kinetics,physicochemical properties and sensory attributes of yoghurts prepared from mixtures of goat and buffalo milks

Five formulations of set‐type yoghurt were produced using different caprine–bubaline milk ratios. They were investigated in regard to the acidification kinetics, yoghurt composition, rheology and sensory attributes. The acidification profile of all five experimental groups was similar, but the maximum acidification rate was higher for yoghurts of milk mixtures. The addition of buffalo milk increased total solids, fat and overall acceptance of yoghurt, besides decreasing synaeresis. Yoghurts made from caprine–bubaline milk mixtures reached good sensory scores and yoghurt prepared with 30% of goat milk and 70% of bubaline milk received the best sensory scores.     

The effects of using transglutaminase,exopolysaccharide‐producing starter culture and milk powder on the physicochemical,sensory and texture properties of low‐fat set yoghurt

This study focused on the effects of transglutaminase (TGase), exopolysaccharide (EPS)‐producing starter culture or skim milk powder addition on some properties of low‐fat set yoghurt. The incorporation of TGase to yoghurt did not affect the acidity of the experimental samples. However, the proteolytic activity of the starter culture significantly decreased in TGase‐treated yoghurt. Addition of TGase to yoghurt with a low dry matter content (11.08%) resulted in low serum separation and gel firmness and viscosity close to those of yoghurt with a higher dry matter content (14.81%). According to the sensory results, it would be possible to produce an acceptable product with a low dry matter and low fat content using TGase. The results shown that the use of EPS‐producing starter cultures for the purpose of improving the texture properties of low dry matter content yoghurt could not be recommended.     

Influence of skimmed milk concentrate replacement by dry dairy products in a low fat set‐type yoghurt model system. I: Use of whey protein concentrates,milk protein concentrates and skimmed milk powder

Ten commercial samples of dry dairy products used for protein fortification in a low fat yoghurt model system at industrial scale were studied. The products employed were whey protein concentratres, milk protein concentrates, skimmed milk concentrates and skimmed milk powder which originated from different countries. The gross chemical composition of these dried products were determined, including polyacrylamide gel electrophoresis (SDS‐PAGE) and isoelectric focusing of the proteins, and minerals such as Na, Ca, K and Mg. Yoghurts were formulated using a skim milk concentrated as a milk base enriched with different dry dairy products up to a 43 g kg⁻¹ protein content. Replacement percentage of skim milk concentrated by dry dairy products in the mix was between 1.49 and 3.77%. Yoghurts enriched with milk protein concentrates did not show significantly different viscosity (35.12 Pa s) and syneresis index (591.4 g kg⁻¹) than the two control yoghurts obtained only from skimmed milk concentrates (35.6 Pa s and 565.7 g kg⁻¹) and skimmed milk powder (32.77 Pa s and 551.5 g kg⁻¹), respectively. Yoghurt fortified with the whey protein concentrates, however, was less firm (22.59 Pa s) and had less syneresis index (216 g kg⁻¹) than control yoghurts. Therefore, whey protein concentrates may be useful for drinking yoghurt production. © 1999 Society of Chemical Industry     

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.     

Effects of cross-linked inulin with different polymerisation degrees on physicochemical and sensory properties of set-style yoghurt

This work investigated effects of cross-linked inulin with different degrees of polymerisation (DP, average = 7 and 15) on physicochemical and sensory properties of set-style yoghurt. Compared with set-style yoghurt made with native inulin (average DP = 4 and 11), yoghurts with cross-linked inulin had higher acidity and lower syneresis values, with a shelf-life of 14 days. Supplementation of cross-linked inulin with higher DP resulted in enhanced firmness and adhesiveness of yoghurts. In addition, bacterial counts showed that yoghurts with cross-linked inulin exhibited longer retention of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus cell viability than that with native inulin. Sensory evaluation indicated that yoghurt with cross-linked long-chain inulin received higher scores for overall acceptability than other samples. However, different types of inulin did not significantly affect odour and colour of set-style yoghurt. Consequently, cross-linked inulin prepared can be exploited as a prebiotic to prolong shelf-life of yoghurt.     

Inulin-enriched dairy desserts: Physicochemical and sensory aspects

The aim of this work was to study how adding inulin of different average chain lengths (long-chain, native, and short-chain inulin) at a concentration of 7.5% (wt/wt) would affect the physicochemical and sensory characteristics of starch-based dairy desserts formulated with either skim or whole milk. The results have shown that the effect of adding 7.5% inulin of different average chain length can give rise to products with different rheological behavior and different sensory characteristics. The skim milk sample with long-chain inulin and the whole milk sample without inulin showed similar flow behavior. Both samples were perceived to have the same creaminess and consistency intensity, but addition of long-chain inulin increased roughness intensity and, consequently, the sensory quality could be negatively affected. The information obtained may be of great interest in designing new products with nutritional and sensory characteristics that meet consumer demands.     

Encapsulation in an alginate–goats’ milk–inulin matrix improves survival of probiotic Bifidobacterium in simulated gastrointestinal conditions and goats’ milk yoghurt

In this work, a new encapsulating matrix, alginate–goats’ milk–inulin, was used to encapsulate Bifidobacterium animalis subsp. lactis BB‐12. The addition of inulin resulted in capsules with a compact structure, and a higher probiotic cell count under simulated gastrointestinal conditions and in probiotic goats’ milk yoghurt during refrigerated storage. Encapsulation of the probiotic bacteria led to slower post‐acidification yoghurts. The results of this study showed that the alginate–goats’ milk–inulin matrix has potential to be used as a new encapsulation material to encapsulate probiotics for use in goats’ milk‐based probiotic fermented dairy products, avoiding the cross‐contamination caused by using capsules based on cows’ milk.