Effects of adding potassium iodate to milk before UHT treatment: I. Reduction in the amount of deposit on the heated surfaces

Abstract

Additions of potassium iodate to milk at 0-05 and 0 -l DIM (10 and 20 ppm) before UHT treatment markedly reduced the rate at which pressure built up during processing. This permitted the use of longer processing times before unacceptable pressures were reached in the heat exchangers. Iodate reduced the amount of protein deposited, particularly in the higher temperature sections of the plant, but had no effect on the deposition of minerals. The more compact nature of the highly mineral deposits offered less resistance to the flow path. Reduction in the amount of protein deposited is likely to be caused by increased denaturation of /?-lactoglobulin and oxidation of heat activated sulphydryl groups by the iodate, thus reducing the formation of high molecular weight polymers of sulphur-containing proteins at the heated surfaces. Increasing the level of sulphydryl groups in the milk through the addition of L-cysteine-HCl caused an increase in the amount of deposit formed during UHT treatment. Whilst little detrimental effect on the quality of the milk resulted from additions of iodate at 005 DIM, milks with 01 mM-iodate became bitter during subsequent aseptic storage. Bitterness was a result of iodate-induced proteolysis of casein.The operating time of an indirect heat ultra-high-temperature (UHT) milk treatment plant is limited by the deposition of milk solids on the heated surfaces. Unacceptable pressures build up in the heat exchangers and the thermal efficiency of the plant is reduced (Burton, 1968). The deposits formed during the heating process have been examined by Ito, Sato & Suzuki (1962a, b) and by Lyster (1965). They found that most of the deposit formed in sections of the heat exchanger operating at temperatures of 100-105 °C and consisted largely of protein (50-60 %) and minerals (30-35%). In higher-temperature sections of the heat exchanger the deposit had an increased mineral content (70%) associated with less protein (15-20%). Small amounts of fat were present (4-8%) in deposits throughout the plant.Fore-warming of the milk at temperatures of 85-95 °C greatly reduced the rate at which deposit was formed, especially in the lower temperature sections of the UHT plant (Bell & Sanders, 1944;Lyster, 1965;Burton, 1966). This effect has been attributed to the denaturation of soluble proteins and the precipitation of Ca phosphate in the milk before it reaches a heated surface.

Adsorption during Heat Treatment Related to the Thermal Unfolding/Aggregation of β-Lactoglobulins A and B

“…5c and 5d), giving rise to a difference in the formation rate of aggregates. with the results of Skudder et al (14) who found that a reduction of free sulfydryl groups in milk markedly reduced This is in agreement with the findings that bulk reactions are rate limiting in the fouling process (15). Arnebrant et the amount of protein adsorbed.…”

A computer based solution to check the drop in milk outlet temperature due to fouling in a tubular heat exchanger

“…Fouling not only results in higher operating costs but has an adverse effect on environment also (Brinkmann, 1986;Graßhoff, 1997;Sandu & Singh, 1991;. Various factors influencing the deposit formation in UHT processing include fore-warming of milk (Bell & Senders, 1944;Lyster, 1965;Burton, 1966;Mottar & Moermans, 1988;Patil & Reuter, 1986a, 1986b, prepasteurization (Lalande, Tissier, & Corrieu, 1984), pH of milk (Burton, 1966;Gordon, Hankinson, & Carver, 1968;Gynning, Thome, & Samuelsson, 1958;Kastanas, Lewis, & Grandison, 1995;Patil & Reuter, 1988;Skudder, Brooker, Bonsey, & Alvarez Guerrero, 1986), air content (Jeurnink, 1995;Tirumalesh, Rao, & Jayaprakash, 1997), surface material (Foster, Britten, & Green, 1989;Foster & Green, 1990;Jeurnink, Verheul, Cohen, & de Kruif, 1996;Sharon & Fuller, 1994;Visser, Jeurnink, Schraml, Fryer, & Delplace, 1997) total solids, age of milk, season, addition of oxidizing agents (iodate, H 2 O 2 , dichromate) (Marshall, 1986;Skudder, Thomas, Pavey, & Perkin, 1981), addition of free fatty acids (Al-roubale & Burton, 1979), addition of phosphates (Burdett, 1974), etc. A number of attempts have been made earlier to cope with the problem of fouling which include design of fouling resistant equipment i.e.…”

Protein stability function relations: native ?-lactoglobulin sulphhydryl-disulphide exchange with PDS

“…11,12 Oxidation of SH groups by iodate reduces deposit formation during ultrahigh-temperature (UHT) treatment of milk. 13 Mottram et al 14 demonstrated that changes in thē avour threshold of disulphide compounds such as bis-2-furanylmethyl disulphide may be due to SH± disulphide interchange with proteins.…”