Achyut Mishra

Maintaining functional integrity during ultrafiltration-based concentration of milk protein concentrate (MPC) is as critical as achieving high solids in the retentate. Previous studies demonstrated that ultrafiltration in plate-and-frame filtration (PF) modules can effectively concentrate MPC derived from spiral-wound ultrafiltration (UF) of skim milk, particularly at elevated temperatures. This study compares the functionality of powdered MPCs produced via UF and PF systems. Skim milk retentate from UF containing 20% total solids and approximately 80% protein on dry basis (feed) was processed using PF modules equipped with flat-sheet membranes across 3 replicates. Three PF treatments were applied: PF22 at 22°C, PF50MS at 50°C targeting medium solids, and PF50HS at 50°C targeting high solids. Filtration for PF22 and PF50HS continued until transmembrane pressure reached 900 kPa, while PF50MS was terminated upon achieving ∼30% solids. Retentates from UF, PF22, PF50MS, and PF50HS were spray-dried and evaluated for rheological and functional properties. All reconstituted MPC powders exhibited pseudoplastic behavior, best described by the Herschel-Bulkley model. Functional assessments revealed that rennet coagulation time increased with PF temperature, necessitating the addition of ∼0.25% CaCl₂ to achieve timely coagulation. Elevated PF temperatures negatively affected other functional attributes, including increased wetting time, reduced solubility, and shortened heat coagulation time-most notably in PF50HS compared with PF22 and UF. Conversely, high-temperature PF enhanced emulsion stability without altering emulsion formation. All PF treatments improved foaming capacity while maintaining comparable foaming stability to UF. A slight reduction in whey protein content and increased protein denaturation was observed at higher PF temperatures. These findings underscore the importance of temperature optimization in preserving the functional properties of MPC during PF concentration.

In the typical milk protein concentrate (MPC) manufacturing process, skim milk is ultrafiltered using a spiral-wound membrane to produce MPC80 with ~20% total solids (TS) and 80% total protein (TP) on a DM basis. However, improving the production efficiency by achieving higher solids in the retentate has been a challenge when using spiral-wound membranes due to the limitation of operating pressure. We attempted flat-sheet UF membrane in a plate-and-frame (PF) module to concentrate the MPC further and achieve better production efficiency. Three replicates of ultrafiltered skim milk (feed) from spiral-wound UF membrane were concentrated in 3 different PF settings, including PF at 22°C (PF22), PF at 50°C for medium solids (PF50MS), and PF at 50°C for high solids (PF50HS). Hence there were total 4 treatments: feed, PF22, PF50MS, and PF50HS. Filtration was carried out until the pressure drop reached 900 kPa for PF22 and PF50HS. For the PF50MS, the filtration was stopped when the TS achieved close to 30%. The average permeate flux and final TS were significantly higher for the treatments conducted at 50°C compared with 22°C with permeate fluxes of 8.76, 10.50, and 11.18 Lm^-2h^-1 and TS of 26.83, 29.92, and 34.24%, respectively, for the PF22, PF50MS, and PF50HS treatments. The apparent viscosity of the final retentates was 577; 1,513; and 12,805 cP at a constant shear rate of 100 s^-1 for the PF22, PF50MS, and PF50HS treatments, respectively. Standard plate count increased in the high-temperature PF retentates; however, the level was below the acceptable limit as described in the USDA standards for fluid milk. This study determined that PF temperature is an important parameter for improving the filtration performance of MPC. The study establishes guidelines for increasing TS and protein levels in dairy foods production.

The performance of nanofiltration (NF) as influenced by hydrodynamic cavitation (HC) and filtration temperature during the concentration of milk protein concentrate (MPC) was investigated. Pasteurised skim milk was concentrated using ultrafiltration (UF) to prepare UF retentate (MPC80, 20% total solids, TS), which was then further concentrated using NF at 22°C and 50°C with or without HC treatments until permeate flux declined to 0.1 L/m²/h. Results showed that UF retentate can be concentrated to higher TS (up to 31.5%) at higher filtration temperature or by applying HC, with synergistic effect in combination of both treatments, during NF.

The aim of this study was to examine the effects of degree of milling on various rice parameters such as proximate composition, and cooking properties using mathematical model. The experiments were performed in the laboratory of Food Research Division, Nepal Agricultural Research Council. The three different medium type rice varieties of Nepal (Lumle-2, Chhomrong and Machhapuchre-3) were exposed to five different degrees of milling (0%, 6%, 8%, 10% and 12%). The degree of milling (DM) level significantly (P≤0.05) affected the milling recovery; head rice yield, nutrient content as well as cooking properties of the rice. Increase in DM resulted in further reduction of protein content, fat content, minerals, milled rice and head rice yield after bran layer was further removed. A positive correlation between DM used in present model, amylose content, kernel elongation and gruel solid loss was observed, however, with an increase in DM; amylose content, kernel elongation and gruel solid loss were found to be increased. Adopting 6 to 8% DM for commercial milling of rice might help to prevent quantitative, qualitative and nutritional loss along with retention of good cooking characteristics.

Sisnu (nettle buds) of variety Urtica plaviflora, an under explored herb of Himalayan region, was preserved by fermentation followed by drying process and quality was evaluated. Chemical analyses of fresh Sisnu was found to be 84.4% moisture, 3.64g crude protein, 4.15g ash, 1.66g fiber, 0.52g fat, 64.10mg potassium, 23.65mg calcium, 17.17mg Sodium and 32.12mg iron per 100g samples on dry basis. The protein and potassium contents were found approximately six times higher than other leafy vegetables. In fermented product, ash, calcium and potassium contents were decreased significantly (p0.05) but flavor and test of salt and or sugar added products were significantly different (p<0.05) from the control. J. Food Sci. Technol. Nepal, Vol. 6 (114-117), 2010 DOI: http://dx.doi.org/10.3126/jfstn.v6i0.8272