Investigation into the Concentrations and Sources of Nitrates and Nitrites in Milk and Plant-Based Powders

Abstract

Milk powders in the United States (US) may contain nitrates and nitrites from several potential sources. These sources include the ingestion of nitrates and nitrites by dairy cows during grazing and drinking, nitric acid used during the sanitization of dairy equipment, and the production of nitrous oxides in directly heated spray dryers. Recently, milk powders manufactured in the US have been rejected during import to other countries due to having nitrite concentrations greater than 2 mg/kg (ppm). To date, the concentrations of nitrates and nitrites in milk and plant-based powders in the US is unknown. In this study the nitrate and nitrite concentrations present in diverse milk powders was investigated including 81 milk powders from local and online retailers from 2015-2018. In addition, 71 commercial milk powders were obtained from blinded production facilities. Nitrate and nitrite concentrations were determined using ion chromatography with conductivity and UV detection. A subset of samples was analyzed for N-nitrosodimethylamine (NDMA) using gas chromatography mass spectrometry (GC-MS). Carbon and nitrogen bulk isotope ratios analyzed using isotope ratio mass spectrometry (IRMS) were used to obtain some insight into the production method (organic vs. conventional) and geographic source of the milk powder samples. Background nitrate concentrations in US produced milk powder samples averaged 17 ± 12 mg/kg. Nitrite was detected at concentrations greater than 2 mg/kg in 5 out of 39 different brands of retail milk and plant-based powders. Of these brands, two were plant-based (soy, coconut) powders and the other three had consistently high nitrites. The analysis of milk powders using stable isotope analysis revealed further information about the cow's diet.