Effect of preservatives on the accuracy of mid-infrared milk component testing

Abstract

Our objective was to determine the effect of commonly used milk preservatives on the accuracy of fat, protein, and lactose content determination in milk by mid-infrared (mid-IR) milk analysis. Two producer raw milks (Holstein and Jersey) and 2 pasteurized modified milks, 1 similar to Holstein milk and 1 similar to Jersey milk were used as the 4 different milk sources. Seven different milk preservative approaches (K(2)Cr(2)O(7) and 6 different bronopol-based preservatives) and a portion of unpreserved milk for each of the 4 different milks sources were tested for fat B, lactose, protein, and fat A. The experiment was replicated 3 times (28 d each) for a total of 84 d. Two mid-infrared (mid-IR) transmittance milk analyzers (an optical and a virtual filter instrument) were used. A large batch of pilot milk was prepared from pasteurized, homogenized, unpreserved whole milk, split into vials, quick frozen by immersion in liquid nitrogen, and transferred into a -80 °C freezer. Pilots were thawed and analyzed on each testing day during the study. Significant increases were observed in all uncorrected readings on the pilot milks over the 84 d of the study, but the increases were gradual and small on each instrument for all components. Results from the study were corrected for these changes. A significant difference in mid-IR fat A readings was observed, whereas no differences were detected for fat B, lactose, or protein between unpreserved and preserved milks containing 0.02% K(2)Cr(2)O(7.) Therefore, K(2)Cr(2)O(7) has little or no effect on mid-IR test results. All bronopol-based preservative approaches in this study differed in mid-IR test results compared with K(2)Cr(2)O(7)-preserved and unpreserved milks, with the largest effect on protein results. Mid-IR uncorrected readings increased with time of refrigerated storage at 4°C for all preservative approaches, with the largest increase for protein. The rate of increase in uncorrected readings with time of storage was always higher for raw milks than for pasteurized milks, and the stability of instrument zero was lower for raw milks than for pasteurized milks. The largest economic effect of a systematic bias caused by a preservative occurs when the milks used for calibration and routine testing for payment do not contain the same preservative or when calibration milks are preserved and milks for routine testing are unpreserved. These effects can create errors in payment for large dairy processing plants ranging from several hundred thousand to over a million dollars annually.

Preservation of Milk and Milk Products for Analytical Purposes

“…When added to milk, pure bronopol, unlike mercuric chloride and potassium dichromate, produces no change in color. (79) However, there are some contradictory reports on the effect of bronopol on the analysis of milk components.…”

“…Barbano et al (79) studied the effect of bronopol (0.02%) on the accuracy of cow milk components by mid-infrared testing and reported a significant difference in all components, with the largest effect on protein content. Conversely, no change in fat and protein readings was detected over 4-week periods, but a significant change (i.e., 0.02-0.03%) in lactose reading occurred.…”

“…It has several advantages over the use of other preservatives; for example, it is noncorrosive, nontoxic, stable at normal storage conditions, and does not produce any color when added in milk, unlike mercuric chloride and potassium dichromate. (79) Bronopol received considerable attention when it was used in its traditional and wellestablished antibacterial concentration of 0.02% (by weight), as it performs efficiently as a sample preservative and does not interfere with the normal testing procedures.…”

Preparation and stability of milk somatic cell reference materials

“…The final SCC of the high SCC skim and whole milk stock solutions ranged from 1 million to 1.3 million somatic cells per mL across replicates. Bronopol was added as a preservative (0.01% mass/ mass; Barbano et al, 2010), and samples of the 2 high …”

Quality changes in milk adulterated with detergent, urea, ammonium sulphate and neutralizers

“…These compounds are used to prepare so called synthetic milk (Chagas et al, 2007). Addition of preservatives such as dichromate, salicylic acid, neutralizer and hydrogen peroxide to milk have the objective of inhibiting or delaying the growth of microorganisms in liquid milk (Barbano et al, 2010 andSouza et al, 2014). The detection methods are difficult to implement in local production and packaging.…”