Stability and expression of K-ras mimotopes in freeze-dried recombinant Lactococcus lactis NZ3900-fermented milk powder during storage in vacuum packaging

AIMS

This study aims to evaluate the storage stability of the freeze-dried recombinant Lactococcus lactis NZ3900-fermented milk powder expressing K-ras (Kristen rat sarcoma viral oncogene homolog) mimotopes targeting colorectal cancer in vacuum packaging.

METHODS AND RESULTS

The freeze-dried L. lactis-fermented milk powder stored in 4-ply retortable polypropylene (RCPP)-polyamide (PA)-aluminium (AL)-polyethylene terephthalate (PET) and aluminium polyethylene (ALPE) was evaluated throughout 49 days of accelerated storage (38°C and 90% relative humidity). The fermented milk powder stored in 4-ply packaging remained above 6 log10 CFU g-1 viability, displayed lower moisture content (6.1%), higher flowability (43° angle of repose), water solubility (62%), and survivability of L. lactis after simulated gastric and intestinal digestion (>82%) than ALPE packaging after 42 days of accelerated storage. K-ras mimotope expression was detected intracellularly and extracellularly in the freeze-dried L. lactis-fermented milk powder upon storage.

CONCLUSIONS

This suggests that fermented milk powder is a suitable food carrier for this live oral vaccine.

Delivery of encapsulated bioactive compounds within food matrices to the digestive tract: recent trends and future perspectives

Encapsulation technologies have achieved encouraging results improving the stability, bioaccessibility and absorption of bioactive compounds post-consumption. There is a bulk of published research on the gastrointestinal behavior of encapsulated bioactive food materials alone using in vitro and in vivo digestion models, but an aspect often overlooked is the impact of the food structure, which is much more complex to unravel and still not well understood. This review focuses on discussing the recent findings in the application of encapsulated bioactive components in fabricated food matrices. Studies have suggested that the integration of encapsulated bioactive compounds has been proven to have an impact on the physicochemical characteristics of the finished product in addition to the protective effect of encapsulation on the fortified bioactive compound. These products containing bioactive compounds undergo further structural reorganization during digestion, impacting the release and emptying rates of fortified bioactive compounds. Thus, by manipulation of various food structures and matrices, the release and delivery of these bioactive compounds can be altered. This knowledge provides new opportunities for designing specialized foods for specific populations.

Rheological Properties of Goat Milk Coagulation as Affected by Rennet Concentration, pH and Temperature

Various factors affect rennet coagulation and consequently cheese yield, but the subject of research has been mainly the cow milk. For the purpose of goat cheese production optimization, this paper investigated the influence of enzyme concentration (0.01–0.054 g/L), pH (6.5–6.1) and temperature (27–35 °C) on rennet coagulation of goat milk. Coagulation time (RCT), aggregation rate (AR), and gel firmness (G’60 and GF), were measured by oscillatory rheometry. The decrease in rennet concentration extended RCT. At lower rennet concentrations, a lower AR was recorded, which ranged from 0.02 Pa/s to 0.05 Pa/s. The decrease in pH from 6.5 to 6.1 caused a two times shorter RCT, and a two times faster AR. There was no effect of pH on the firmness of the rennet gel. The increase in coagulation temperature from 27 °C to 35 °C reduced the RCT of pasteurized milk from 12.6 min to 8.6 min, and caused a linear increase in the AR, but did not significantly affect the firmness of the gel. The present study revealed that the optimization of the rennet coagulation process could be directed towards pH lowering, or temperature increase, since they accelerate the process, but do not alter the examined gel firmness parameters.

Valorization of Concentrated Dairy White Wastewater by Reverse Osmosis in Model Cheese Production

Treatment of dairy white wastewater (WW) by reverse osmosis (RO) is usually performed to generate process water and to reclaim dairy components for their valorization. For this study, a mixture of pasteurized milk and WW from a dairy plant was concentrated by RO to achieve a protein concentration similar to that of skimmed milk. Retentates, which are concentrated WW, were used in the preparation of cheese milk. The effect of using model concentrated WW was evaluated on (1) the soluble–colloidal equilibrium between protein and salt, (2) the milk-coagulation kinetics, and (3) the cheese composition and yield. An economic assessment was also carried out to support the decision-making process for implementing a new RO system in a dairy plant for the valorization of dairy WW. The results showed that substituting more than 50% of the amount of cheese milk with model pasteurized WW concentrates decreased the moisture-adjusted cheese yield and impaired the coagulation kinetics. Excessive cheese moisture was observed in cheeses that were made from 50% and 100% model WW concentrates, correlating with a change in the soluble–colloidal equilibrium of salts, especially in calcium. To achieve sustainable and economic benefits, the ratio of added WW concentrates to cheese milk must be less than 50%. However, for such an investment to be profitable to a dairy plant within 0.54 years, a large-size plant must generate 200 m3 of WW per day with at least 0.5% of total solids, as the economic analysis specific to our case suggests.

New Insights into Cheese Microstructure

Microscopy is often used to assist the development of cheese products, but manufacturers can benefit from a much broader application of these techniques to assess structure formation during processing and structural changes during storage. Microscopy can be used to benchmark processes, optimize process variables, and identify critical control points for process control. Microscopy can also assist the reverse engineering of desired product properties and help troubleshoot production problems to improve cheese quality. This approach can be extended using quantitative analysis, which enables further comparisons between structural features and functional measures used within industry, such as cheese meltability, shreddability, and stretchability, potentially allowing prediction and control of these properties. This review covers advances in the analysis of cheese microstructure, including new techniques, and outlines how these can be applied to understand and improve cheese manufacture.

Different Thermal Treatment Methods and TGase Addition Affect Gel Quality and Flavour Characteristics of Decapterus maruadsi Surimi Products

Decapterus maruadsi surimi products were prepared using the thermal treatment methods of boiling (BOI), steaming (STE), back-pressure sterilization (BAC), roasting (ROA), microwaving (MIC), and frying (FRI), respectively. The effect of glutamine transaminase (TGase) addition was also investigated. The moisture distribution, water retention, microstructure, color, fracture constant, protein secondary structure, chemical forces, and flavor components of each sample were determined. The differences in gel and favor characteristics between D. maruadsi surimi products caused by thermal treatment methods were analyzed. The results showed that BOI, STE, and FRI had the largest protein secondary structure transitions and formed dense gel structures with high fracture constant. The kinds of flavour components in BOI and STE were completer and more balanced. The high temperature treatment available at BAC and FRI (110 °C and 150 °C) accelerated the chemical reaction involved in flavor formation, which highlighted the flavor profiles dominated by furans or esters. The open thermal treatment environments of ROA, MIC, and FRI gave them a low moisture content and water loss. This allowed the MIC to underheat during the heat treatment, which formed a loose gel structure with a low fracture coefficient. The addition of TGase enhances the gel quality, most noticeably in the ROA. The aldehyde content of the FRI was enhanced in the flavor characteristic. The effect of adding TGase to enhance the quality of the gel is most evident in ROA. It also substantially increased the content of aldehydes in FRI. In conclusion, different heat treatments could change the gel characteristics of surimi products and provide different flavor profiles. The gel quality of BOI and STE was consistently better in all aspects.

Derivation of multivariate indices of milk composition, coagulation properties, and curd yield in Manchega dairy sheep

This study approaches the interrelation patterns between composition of milk and whey, curd yield, chromaticity, syneresis, and technological quality of Manchega sheep milk using multivariate factor analysis. In addition, the effect of the main husbandry components (flock, prolificacy, season of the year, stage of lactation, and parity) on the common latent factors that define the pattern of variation of Manchega milk was assessed. For this purpose, 1,200 individual Manchega ewe milk samples from 4 different flocks registered under the Protected Designation of Origin Queso Manchego were analyzed (50 ewes/flock). Samples were collected in 2 different seasons of the year (spring and autumn) and at 3 time points per season: early, mid-, and late lactation. The obtained results suggested that curd yield mainly depends on milk composition, and the retention of water in the curd is related to coagulation traits. Thus, composition and moisture content could be useful indicators to assess the efficiency and quality of milk intended for cheesemaking, regardless of the analysis of coagulation properties. Finally, in terms of husbandry, a direct effect of flock and stage of lactation was observed on all analyzed factors, with a lower influence of season and parity.

Composition and properties of bovine milk: A study from dairy farms in northern Sweden; Part II. Effect of monthly variation

This study investigated the influence of monthly variation on the composition and properties of raw farm milk collected as part of a full-scale cheese-making trial in a region in northern Sweden. In our companion paper, the contribution of on-farm factors to the variation in milk quality attributes is described. In total, 42 dairy farms were recruited for the study, and farm milk samples were collected monthly over 1 yr and characterized for quality attributes of importance for cheese making. Principal component analysis suggested that milk samples collected during the outdoor period (June-September) were different from milk samples collected during the indoor period. Despite the interaction with the milking system, the results showed that fat and protein concentrations were lower in milk collected during May through August, and lactose concentration was higher in milk collected during April through July than for the other months. Concentrations of free fatty acids were generally low, with the highest value (0.86 mmol/100 g of fat) observed in February and the lowest (0.70 mmol/100 g of fat) observed in June. Plasmin and plasminogen-derived activities varied with sampling month without a clear seasonal pattern. The pH of farm tank milk ranged from 6.60 to 6.82, with the lowest and highest values in September and February, respectively. The highest somatic cell count was observed in August (201 × 10³ cells/mL) and the lowest in April (143 × 10³ cells/mL). The highest value of gel strength, was recorded in December (88 Pa) and the lowest in July (64 Pa). Rennet coagulation time and gel strength were inversely correlated, with the lowest rennet coagulation time value observed in December. Orthogonal projections to latent structures (OPLS) and discriminant analysis adaptation of OPLS identified casein micelle size and total proteolysis as the milk quality attributes with major responses to sampling month, with smaller casein micelle size and higher total proteolysis associated with the outdoor months. Using discriminant analysis adaptation of OPLS to further investigate causes behind the variation in milk traits revealed that there were factors in addition to feeding on pasture that differed between outdoor and indoor months. Because fresh grass was seldom the primary feed in the region during the outdoor period, grazing was not considered the sole reason for the observed difference between outdoor and indoor periods in raw milk quality attributes.

Rheology and Microstructures of Rennet Gels From Differently Heated Goat Milk

Rennet coagulation of goat milk heated to 65 °C/30 min (Gc), 80 °C/5 min (G8) and 90 °C/5 min (G9) was studied. A rheometer equipped with a vane geometry tool was used to measure milk coagulation parameters and viscoelastic properties of rennet gels. Yield parameters: curd yield, laboratory curd yield and curd yield efficiency were measured and calculated. Scanning electron microscopy of rennet gels was conducted. Storage moduli (G') of gels at the moment of cutting were 19.9 ± 1.71 Pa (Gc), 11.9 ± 1.96 Pa (G8) and 7.3 ± 1.46 Pa (G9). Aggregation rate and curd firmness decreased with the increase of milk heating temperature, while coagulation time did not change significantly. High heat treatment of goat milk had a significant effect on both laboratory curd yield and curd yield. However, laboratory curd yield (27.7 ± 1.84%) of the G9 treatment was unreasonably high compared to curd yield (15.4 ± 0.60%). The microstructure of G9 was notably different compared to Gc and G8, with a denser and more compact microstructure, smaller paracasein micelles and void spaces in a form of cracks indicating weaker cross links. The findings of this study might serve as the bases for the development of different cheese types produced from high-heat-treated goat milk.

Understanding the differences in cheese-making properties between reverse osmosis and ultrafiltration concentrates

Concentrating milk by reverse osmosis (RO) has the potential to increase cheese yield but is known to impair cheese-making properties. The main compositional differences between ultrafiltration (UF) and RO concentrates are the high lactose and mineral contents of the latter. The objective of this work was to determine the distinct effects of high lactose and high minerals on the cheese-making properties of RO concentrate, by supplementing UF concentrate with lactose. The soluble colloidal equilibria of concentrates were studied as well as several other properties: rennet gelation behavior, cheese mass balance, composition, and microstructure. Rennet coagulation time was longer and gel firming rate was lower for RO concentrate than for UF concentrate. Lactose was mainly responsible for these differences. Lactose in RO concentrate was also responsible for the 7% increase of moisture-adjusted cheese yield, relative to UF concentrate. Compared with cheese made from UF concentrate, cheese made from RO concentrate showed higher moisture content, which could not be attributed to lactose but to the high mineral concentration. This study showed the potential of using RO instead of UF concentrate to maximize cheese yield. The approach is, however, limited to applications where post-acidification can be controlled, and will require appropriate strategies to reduce the negative effects of high mineral content in RO concentrate.

Processing milk causes the formation of protein oxidation products which impair spatial learning and memory in rats

This study explored the effects of protein oxidation during milk processing on spatial learning and memory in rats. Increasing the heating time, fat content, and inlet air temperature during processing by boiling, microwave heating, spray-drying, or freeze-drying increases milk protein oxidation. Oxidative damage done to milk proteins by microwave heating is greater than that caused by boiling. Dityrosine (DT), as a kind of tyrosine oxidation product, is the most important marker of this process, especially during spray-drying. Rats received diets containing either SWM (spray-dried milk powder diet), FWM (freeze-dried milk powder diet), FWM + LDT (freeze-dried milk powder + low dityrosine diet, DT: 1.4 mg kg-1), or FWM + HDT (freeze-dried milk powder + high dityrosine diet, DT: 2.8 mg kg-1) for 6 weeks. We found that the SWM group, the FWM + LDT group, and the FWM + HDT group appeared to have various degrees of redox state imbalance and oxidative damage in plasma, liver, and brain tissues. Further, hippocampal inflammatory and apoptosis genes were significantly up-regulated in such groups, while learning and memory genes were significantly down-regulated. Eventually, varying degrees of spatial learning and memory impairment were demonstrated in those groups in the Morris water maze. This means that humans should control milk protein oxidation and improve the processing methods applied to food.