Abstract
Thermal treatments of dairy products favor oxidations, Maillard reactions, and the formation of sugar or lipid oxidation products. Additives including flavorings might enhance these reactions or even induce further reactions. Here we aimed to characterize protein modifications in four flavored milk drinks using samples along the production chain—raw milk, pasteurization, mixing with flavorings, heat treatment, and the commercial product. Therefore, milk samples were analyzed using a bottom up proteomics approach and a combination of data-independent (MSE) and data-dependent acquisition methods (DDA). Twenty-one small carbonylated lipids were identified by shotgun lipidomics triggering 13 protein modifications. Additionally, two Amadori products, 12 advanced glycation end products (AGEs), and 12 oxidation-related modifications were targeted at the protein level. The most common modifications were lactosylation, formylation, and carboxymethylation. The numbers and distribution of modification sites present in raw milk remained stable after pasteurization and mixing with flavorings, while the final heat treatment significantly increased lactosylation and hexosylation in qualitative and quantitative terms. The processing steps did not significantly affect the numbers of AGE-modified, oxidized/carbonylated, and lipid-carbonylated sites in proteins.
Highlights
Bovine milk is an important food in human nutrition as it can be converted into a wide range of products, such as yoghurt, cheese, and various drink types [1]
Using previously-established procedures, the targeted analysis of glycated, advanced glycation end products (AGEs)-modified, carbonylated/oxidized, and low molecular weight (LMW) carbonyl–protein adducts allowed the confident identification of 204 modified peptides (Table S2) corresponding to 189 modification sites in 108 milk proteins
In order to evaluate the influence of the processing chain and the addition of further ingredients such as flavorings on protein modifications, we studied samples collected for cocoa, chocolate, strawberry, and vanilla-flavored milk drinks
Summary
Bovine milk is an important food in human nutrition as it can be converted into a wide range of products, such as yoghurt, cheese, and various drink types [1]. Raw milk is typically heat-treated to increase the microbiological safety and shelf-life [2]. In 2017 around 99% of the raw milk produced in the European Union (EU) was processed with ~11% used to produce milk drinks [3]. Independent of the treatment, the addition of flavorings, such as chocolate, strawberry, or vanilla, is getting more popular. This requires an additional manufacturing step, i.e., addition of flavorings and other ingredients, followed by a final heat treatment prior to packaging and transportation of the products
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