Low-temperature Long-time Treatment Research Articles

Evaluating the effects of different processing methods on the nutritional quality of bovine milk

Milk is a universal food that is widely consumed around the world irrespective of age. It has a complex matrix consisting of proteins, carbohydrates, minerals, vitamins, and enzymes that have successfully retained the interest of researchers as yet. The aim of the study was to evaluate the effect of low-temperature long-time (LTLT), ultraviolet light (UV), and ultrasound (US) treatments on physicochemical properties, microbial count, and fatty acid profiling of three types of bovine milk – Country (C), Jersey (J), and Holstein Friesian (HF). The study was conducted in southern India, where these three types of milk are commonly consumed. It was found that no significant (p ˂ 0.05) differences in the proximate composition of milk samples subjected to different treatments compared to untreated milk. However, LTLT treatment resulted in a reduction in ascorbic acid content and significant changes in antioxidant activity and lactose content. LTLT treatment was also able to kill the pathogenic bacteria E. coli, whereas UV and US treatment only showed a notable reduction in the E. coli count. Fatty acid profiling of the treated milk samples was done using GC/MS, and Fourier Transform Infrared Spectroscopy (FTIR) was performed to study the types of chemical bonds present. The results showed that non-thermal treatments (UV and US) were able to sustain the chemical characteristics of milk and had potential for implementation in the dairy industry. Overall, the study highlights the potential benefits of non-thermal treatments such as UV and US in maintaining the chemical properties of milk and reducing pathogenic bacteria count. The findings could be useful in the dairy industry to ensure the safety and quality of milk.

Radiofrequency-assisted low-temperature long-time (LTLT) pasteurization of onion powder

Recent outbreaks associated with Salmonella in low-moisture foods (LMFs) have urged the necessity to design and implement the pasteurization process. Sugar-rich LMFs, such as dates, confections, and some spices, may show severe quality loss due to the sugar phase transitions and Maillard reactions at elevated temperatures. Low-temperature long-time (LTLT) pasteurization can potentially eliminate pathogens in sugar-rich LMFs without compromising the products' quality. Here, we chose onion powder (water activity 0.32 ± 0.01, moisture content 7.4 ± 0.1%, w.b.); studies documented its foodborne pathogen contamination. Isothermal inactivation studies of Salmonella enterica Enteritidis PT 30 (S. Enteritidis) in onion powder were conducted at 60 °C, 65 °C, and 70 °C. An orthogonal experimental design optimized the radiofrequency (RF) heating parameters of 500 g onion powder. We accomplished the microbial validation study with RF-assisted hot-air pasteurization and assessed the quality changes before and after the process. The cold spot of RF-heated onion powder reached 66 °C within 180 s. We obtained a 3.4-log reduction of S. Enteritidis at 38 h of LTLT treatment, whereas only 2.10-log reductions were obtained in the control group. No significant quality loss was observed in onion powder after the process.

Effect of Pulsed Electric Field (PEF) on Bacterial Viability and Whey Protein in the Processing of Raw Milk

There is growing concern regarding the nutritional value of processed food products. Although thermal pasteurization, used in food processing, is a safe method and is widely applied in the food industry, food products lack quality and nutritional value because of the high temperatures used during pasteurization. In this study, the effect of pulsed electric field (PEF) processing on whey protein content and bacterial viability in raw milk was evaluated by changing the PEF strength and number of pulses. For comparison, traditional pasteurization techniques, such as low-temperature long-time (LTLT), ultra-high temperature (UHT), and microfiltration (MF), were also tested for total whey protein content, bacterial activity, and coliforms. We found that, after treatment with PEF, a significant decrease in total bacterial viability of 2.43 log and coliforms of 0.9 log was achieved, although undenatured whey protein content was not affected at 4.98 mg/mL. While traditional pasteurization techniques showed total bacterial inactivation, they were detrimental for whey protein content: β-lactoglobulin was not detected using HPLC in samples treated with UHT. LTLT treatment led to a significant decrease of 75% in β-lactoglobulin concentration; β-lactoglobulin content in milk samples treated with MF was the lowest compared to LTLT and UHT pasteurization, and ~10% and 27% reduction was observed.

Quality Characteristics and Consumer Acceptance of High-Moisture Mozzarella Obtained from Heat-Treated Goat Milk

High-moisture mozzarella is a pasta filata cheese manufactured from cow or buffalo milk that has spread all over the world. Its manufacturing from the milk of small ruminants (goat and sheep) has been recently proposed to innovate this ailing sector. Previously, a protocol was reported for making goat mozzarella from unpasteurized milk but, according to legislation, the microbiological safety of raw milk fresh cheeses is not guaranteed. In the present research, two new protocols were tested for producing mozzarella from pasteurized milk prepared by two different low-temperature long-time treatments (67 °C or 63 °C × 30 min). The obtained cheeses were subjected to physical–chemical and microbiological analyses and to consumer testing. The results showed that the heat treatments caused longer coagulation times than those reported in the literature, despite pre-acidification (at pH 5.93 or 6.35) having been performed to counterbalance the expected worsening of the coagulation aptitude. The obtained products showed differences in the chemical composition, texture, proteolysis, and lipolysis. Both pasteurization and pre-acidification played a role in determining these variations. Consumer testing indicated that mozzarella obtained from milk heated at the lower temperature and coagulated at a higher pH reached a good level of appreciation (62%).

Exploring optimal strategies for aquatic macrophyte pre-treatment: Sustainable feedstock for biohydrogen production

Aquatic macrophytes; Water hyacinth (Eichhornia crassipes) and Azolla, biomass have certain advantages over terrestrial plant biomass to use as non-edible feed for 2nd generation bioenergy production. This is mainly due to the lower lignin content and higher productivity of aquatic macrophytes. These macrophytes do not require arable land. Present study explored on development of factorial approach based optimal pretreatment process for mild acid hydrolysis of Eichhornia crassipes and Azolla microphylla biomass for conversion to fermentable sugars. The simpler structure of aquatic plants translates to higher sugar recovery using milder pretreatment conditions compared to terrestrial plants. H2SO4 & HCl used in mild concentrations for acid hydrolysis experiments. Approximately, 20% of the dry biomass was recovered as fermentable sugar (mainly xylose) upon treatment with dilute sulphuric acid (0.5–1.5% v/v) or hydrochloric acid (2–4% v/v) at 100–120 °C for 30–60 min. Within this range of parameters, sugar yield followed a simple additive model, implying that a decrease in sugar yield is due to reduction of one parameter. This provides a choice between high temperature short time (HTST) and low temperature long time (LTLT) treatments. HTST requires sophisticated pressure vessels and correspondingly higher capital investment for the advantage of a higher throughput. LTLT treatments can be performed in cost economy manner using relatively simple equipment. For economic, environmental and technical reasons, acid addition should be kept to a minimum, which is possible by a choice of higher temperature and longer treatment time. Such pretreatment may be employed as the first step of a two-step pretreatment process prior to enzymatic saccharification of cellulosic fraction. The acid pre-treated hydrolysate of water hyacinth and Azolla microphylla explored for hydrogen production through dark fermentation process through employment of C5 & C6 sugar utilizing microbe Enterobacter cloacae DT-1 strain.

Effect of low-temperature long-time and high-temperature short-time blanching and frying treatments on the French fry quality of six Irish potato cultivars.

Processing conditions are an important determinant of French fry quality. However, the effect of low-temperature long-time (LTLT) and high-temperature short-time (HTST) blanching and frying treatments has not been investigated in many cultivars. The current study investigates the effect of the sequential application of these treatments on French fries processed from six Irish potato cultivars (Fianna, Innovator, Mondial, Navigator, Panamera and Savanna). Blanching was effected at 75°C for 10min or 85°C for 5min and frying was effected at 160°C for 2min or 180°C for 1min. These treatments resulted in significant differences in the quality of the fries across the cultivars. The blanching treatments had a greater impact on the French fry quality than the frying treatments. LTLT blanching resulted in lower oil (12-13% fresh mass basis [fmb]), and higher protein (3.5-4.3% fmb) and mineral content in the French fries processed from Innovator, compared to HTST blanching. This was accompanied by a crispier crust, which required a greater puncture force (1.2-2.1N) for penetration. Blanching with the LTLT treatment before HTST frying resulted in French fries that were the most acceptable to consumers and these were from Fianna, Innovator and Mondial. The current study demonstrates that the effect of French fry processing conditions is cultivar-dependent.

Low temperature, long time treatment of porcine M. longissimus thoracis et lumborum in a combi steamer under commercial conditions

As the interest in low temperature, long time (LTLT) treatment of meat, as well as the use of modern combi steamer technology is growing, this study characterized the effects of LTLT treatments on porcine Musculus longissimus thoracis et lumborum in a combi steamer. Upon heating for 10 and 20h at 53°C or 58°C, weight loss increased with both time and temperature, while no significant changes over time could be reached between 20 and 30h. Redness only varied with temperature, showing lower a* values at 53°C. Shear force values at 58°C remained at a stable level over time and were lower than values at 53°C after 10 and 20h. In contrast, at 53°C, shear force was reduced with increasing treatment time, until after 30h both temperatures showed similar shear force values. Inoculation experiments revealed that already the lowest LTLT condition (53°C, 10h) inactivated 5 log10 cfu/g of certain indicator pathogens confirming the safety of these treatments.

Sensory characteristics of meat cooked for prolonged times at low temperature

The present study evaluated the sensory characteristics of low temperature long time (LTLT) treated Semitendinosus from pork and beef and Pectoralis profundus from chicken. Semitendinosus and Pectoralis profundus muscles were heat treated at 53°C and 58°C for T c + 6 h, T c + 17 h, and T c + 30 h (only Semitendinosus from pork and beef). T c was the time for the samples to equalize with the temperature in the water bath. Tenderness increased with increasing heating temperature and time in pork and beef, but not in chicken. Juiciness decreased with increasing heating temperature and time in all species, and cooking loss increased with increasing temperature. A done appearance was developed with increasing heating time at 58 °C in pork and beef, while in chicken the done appearance was only affected by temperature. Flavor attributes were less affected by the LTLT treatment for all species.

Protein denaturation and water–protein interactions as affected by low temperature long time treatment of porcine Longissimus dorsi

The relationship between water–protein interactions and heat-induced protein denaturation in low temperature long time (LTLT) treated pork Longissimus dorsi was investigated by combining low-field NMR T 2 relaxometry with DSC measurements and measures of shrinkage of porcine Longissimus dorsi heated to 53 °C, 55 °C, 57 °C and 59 °C for either 3 or 20 h. Water within the myofibrils, measured by NMR T 21 relaxation times, was affected by both temperature and holding time during LTLT treatment between 53 °C and 59 °C. The changes in NMR T 21 relaxation times were associated with decreased fiber diameter and increased cooking loss, revealing a relationship between transverse shrinkage, water–protein interactions and cooking loss. DSC measurements revealed a concomitant decrease in ΔH 68 °C , which suggests impact of collagen denaturation on the retention of water within the meat during LTLT treatment. Furthermore, a decrease in ΔH 75 °C suggested that prolonged cooking (20 h) resulted in actin denaturation leading to decreased T 21 relaxation times and higher cooking loss.

Effect of prolonged heat treatment from 48°C to 63°C on toughness, cooking loss and color of pork

The effect of low temperature long time (LTLT) heat treatment at 48 °C, 53 °C, 58 °C, and 63 °C for T c (time to reach a core temperature equal to the water bath), T c + 5 h holding time, and T c + 17 h holding time was studied in Longissimus dorsi and Semitendinosus muscles from slaughter pigs and sows. Meat toughness (Warner–Bratzler Shear Force), cooking loss and color (Minolta L*a*b*-values) was measured and in the cooking loss the amount of heat-soluble collagen and activity of cathepsin B + L was determined. Decreasing shear force and increasing cooking loss during LTLT treatment was observed between 53 °C and 58 °C. Furthermore, increasing temperature from 53 °C to 58 °C and increasing time from T c to T c + 17 h increased the solubility of collagen. Residual activity of cathepsin B + L in LTLT treated pork was mainly affected by temperature, showing the highest activity at 58 °C and 63 °C.

Quality Evaluation of an Ohmically Cooked Ham Product

Selected parameters (cooking loss, instrumental colour and texture and sensory quality) of a brine-injected pork muscle cooked by a novel and rapid ohmic cooking protocol were examined and compared with those obtained in conventionally cooked samples. Ohmic samples were cooked using either a low-temperature long-time (LTLT) protocol (2 min equilibration, 5 min ohmic heating to 70 °C, 8 min holding) or a high-temperature short-time (HTST) procedure (2 min equilibration, 6 min ohmic heating to 95 °C) performed within a hot air cabinet set at 80 °C (LTLT) and 100 °C (HTST). Conventional cooking (steam oven at 80 °C for 120 min) was conducted to a core temperature of 70 °C. The LTLT treatment gave a much lower cooking loss value (4–5% lower, p < 0.05) than the other treatments, though the full magnitude of this difference was not completely reflected in the proximate composition of the cooked products. Ohmically cooked ham showed a significantly (p < 0.05) lighter surface colour with Hunter L values of 65.3 (LTLT) and 63.5 (HTST) relative to the control (61.4). Texture profile analysis (TPA) indicated a significant difference (p < 0.05) in hardness (N) especially between the HTST surface (82.1 N) and the conventional centre (58.8 N). Although the ohmic cooking protocols yielded products with quite acceptable eating qualities, sensory evaluation found the overall quality of the conventionally cooked ham to be significantly (p < 0.05) superior, indicating that further optimisation of the ohmic cooking protocols would be required prior to any commercial adoption.