International Journal of Dairy Technology

The production of ethanol and beta‐galactosidase by Kluyveromyces marxianus and Saccharomyces fragilis strains grown in cheese whey was evaluated. The conditions for fermentation in 50 g/L (3.3% lactose) and 150 g/L (8.8% lactose) cheese whey were 100 rpm for 24 h at 30, 35 and 40 °C. Saccharomyces fragilis IZ 275 in 8.8% lactose at 40 °C resulted in 3.90% ethanol. Kluyveromyces marxianus CCT 3172 showed higher beta‐galactosidase, 1.10 U/mg, at 30 °C. Therefore, the choice of cultivation conditions and the most suitable species is important for obtaining high yields of the products of interest.

Taste panel data confirm that commercial preparations of Bacillus subtilis neutral proteinase can accelerate flavour development in Cheddar cheese without defect formation. The influence of the enzyme on the rate of ripening can be controlled by varying the cheese storage temperature. Fungal acid proteinase gives bitter cheese without enhancing typical flavour, even when used at concentrations corresponding to 5×and 25× less than the optimum neutral proteinase activity. Bacterial alkaline proteinase and broadspecificity proteinase produced bitter cheese but the latter enzyme also enhanced the intensity of typical flavour.

This study explores drivers and resulting changes in the structure and technical efficiency of Irish dairy farms from 2005 to 2018 (covering pre‐ and post‐milk quotas) during which milk production increased by 54%. Over this period, farm structure changed dramatically (fourfold increase in farmers milking >100 cows) and farmers improved technical efficiency and profitability and reduced the greenhouse gas emission intensity of milk produced. The impact of the adoption of key technologies at farm level and the contribution of strategic direction nationally (the Irish Government's Food Harvest 2020 Strategy) influencing this development are explored as are future sector challenges.

In this study, probiotic fermented milk beverages with black mulberry (MFM), red grape (GFM) and cornelian cherry (CFM) were produced. The viable cell counts of Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus acidophilus and Bifidobacterium lactis were detected within the recommended biotherapeutic levels (>10⁶ log cfu/mL) as a measure of the potential prebiotic effects of the components present in fruit‐based probiotic fermented milk. Variations in the pH, the syneresis and the colour values of the different milks were determined to be significantly different (P < 0.01). The value of the total antioxidant capacity in CFM samples was higher due to the high levels of ascorbic acid and total phenolic compounds. GFM samples had a more favourable taste than the other milks, despite similar overall sensory scores for all the fruit‐based fermented milks. We concluded the probiotic fermented milk drinks produced with black mulberry, red grape and cornelian cherry had high levels of probiotic bacteria and maintained their therapeutic activity during storage. Therefore, fermented milks incorporated with fruit matrices may be an alternative dairy product to deliver probiotic bacteria.

Seven varieties of Cheddar cheese were evaluated using free‐choice and conventional (quantitative descriptive analysis) profiling. This study looks at the odour and flavour attributes of the cheeses; as well as the more widely reported texture characteristics. Generalized Procrustes analysis was used to analyse data from both profile methods, as well as being applied to compare the perceptual spaces obtained from the two methods. The results obtained from both profiling procedures were similar and easily interpretable, suggesting that the less time consuming free‐choice method is an appropriate technique when used with trained assessors. Strength of odour and flavour, and rubbery and grainy texture were some of the important attributes separating the cheeses in a two dimensional perceptual space. Preference judgements were obtained from 50 consumers using a nine point hedonic scale. These data were related to the profile space using Preference Mapping and the best model evaluated.

At present, only two approaches for modifying the composition of bovine milk can be applied in practice: (a) changing to a breed other than the predominant Friesian and (b) dietary manipulation. Although other breeds may produce milk of high fat and protein content, the high yield of the Friesian, allied to the fact that it is an acceptable meat animal, probably ensures its continued dominance. In terms of diet, the content, yield and type of milk fat are easily susceptible to manipulation. However, the specialized diets required for this type of manipulation would probably incur extra costs, and it is not clear if the improved properties of the butter, eg, a butter having better low‐temperature spreadability, could attract a better return in the market. Protein content and yield are fairly insensitive to diet, and the consensus is that protein composition is invariant. Currently, the most sensible strategy for the dairy farmer appears to be to produce milk as cheaply as possible, and to leave it to the technologists to convert the components into a range of attractive, nutritious foodstuffs.

The growth of six probiotic commercial strains of lactobacilli was assessed in reconstituted dried whey and buttermilk supplemented with yeast extract, meat peptone, soy peptone, tryptone or casein acid hydrolysate at 0.3%, 0.6% or 1%. The addition of 1% glucose was also tested. Growth and acidification kinetics were determined at 37°C using MRS broth and a commercial culture medium as references. The suitability of whey and buttermilk as cryoprotectants at –20°C and –70°C was also assessed. Whey and buttermilk with 0.3% yeast extract were chosen for the growth of probiotic lactobacilli, since no satisfactory growth was observed without an external nitrogen source, whereas glucose did not improve the growth of any of the strains assayed. In general, buttermilk performed as satisfactorily as the reference media. The effectiveness of these media as cryoprotectants was strain dependent: skimmed milk and whey were the most suitable ones, especially for long‐term storage at –20°C. However, at –70°C, no significant differences were observed between the culture media assessed. The use of whey or buttermilk as culture media for the production of probiotic lactic acid bacteria and for their cryopreservation implies a novel use of these low‐cost products, offering an alternative way of utilizing the by‐products of the dairy industry, helping to minimize their negative impact on the environment.

Kefir, a slightly acidic fermented milk, is produced by adding lactic acid bacteria and yeasts, in the form of grains, to milk. The bacteria and yeasts present in the kefir grains are known to vary widely. Selective growth media and morphological and biochemical characteristics were used for the isolation and identification of the microbes present in the grains from eight different sources in South Africa. The kefir grains were activated in milk for only 24 h to prevent any changes in the microbial population of the grains. The microbial numbers varied between 6.4 × 10⁴and 8.5 × 10⁸ cfu/g on the media selective for the bacterial species and between 1.5 × 10⁵and 3.7 × 10⁸ cfu/g on the media selective for the yeast species. The bacterial genera that were identified included Lactobacillus, Leuconostoc and Lactococcus and the yeast genera included Zygosaccharomyces, Candida and Saccharomyces. The distribution frequencies of the microbes in the different grains were determined and most of the grains were dominated by two microbial species. No pediococci, acetic acid bacteria or propionibacteria were detected.

This paper presents research on the effect of enzymatic cross‐linking of milk proteins on the properties of yoghurt. Whole milk was incubated with transglutaminase (TG) prior to fermentation (2 h, 40°C, E/S ratio 1/2000). Enzyme action was stopped by heating (1 min, 80°C). Skim‐milk was treated by simultaneous use of TG and thermophilic yoghurt starter culture without inactivation of the enzyme. A TG treatment of milk prior to fermentation led to prolonged fermentation, while the concomitant use of TG and culture had no influence on fermentation time. Post acidification of yoghurt during storage was lower for products from enzyme‐treated milk. This applies both for products cross‐linked prior to fermentation with enzyme inactivation, and for simultaneous use of culture and TG without inactivation of the enzyme. Scanning electron microscopic studies revealed that a TG treatment of milk led to reduced mesh sizes of the protein network, and a more regular distribution of the proteins in the yoghurt gel. As a result, yoghurt products from enzyme‐treated milk showed increased gel strength and less syneresis, especially when the enzyme was not inactivated. Sensory studies revealed that odour and consistency properties of products from TG‐treated milk were assessed as less ‘yoghurt specific’. On the other hand, products from enzyme‐treated milk were described as being more creamy, indicating that a TG treatment may simulate fat in fermented milk products.