Chemical and sensory changes during shelf-life of UHT hydrolyzed-lactose milk produced by “in batch” system employing different commercial lactase preparations

Abstract

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Understanding the effect of storage temperature on the quality of semi-skimmed UHT hydrolyzed-lactose milk: an insight on release of free amino acids, formation of volatiles organic compounds and browning

“…The trend of free glutamic acid instead may confirm the specificity of the proteolytic side activity of the LP towards specific amino residues as well as a positive correlation with the temperature. In a previous work, we showed that the type of amino acids released during "in batch" production does not depend only on the degree of lactase purity, but also on the specificity of the proteolytic activity, as different free amino acids profiles were obtained in UHLMs treated with different lactases (Bottiroli, Troise, et al, 2020). In particular, UHLM produced with the same lactase used in this study caused a significant release of glutamic acid in milk.…”

“…Although in this case glutamic acid was the only amino acid showing this behavior, the result may indicate that, at storage temperature higher than 20 • C, release of free amino acids can still occur in the milk. Previous data taken at 20 • C are on the other hand not in agreement (Bottiroli, Troise, et al, 2020). The fact that glutamic acid is not converted through Strecker degradation may explain also the opposite trend showed at 40 • C by those amino acids involved in the reaction (e.g.…”

“…Jensen et al (2015) studied the off-flavors formation in UHLM during storage in relation to the sensory profile and reported that the formation of specific volatiles organic compounds (VOCs) following Maillard pathways underpins the development of stale flavor. An increase in the concentration of methyl ketones, aldehydes and organic acids during storage appeared as major responsible for the development of this sensory defect in UHLM (Bottiroli, Troise, et al, 2020;Jensen et al, 2015). Our group estimated these VOCs in UHLM both by HS SPME GC-MS and PTR-TOF-MS, outlining that off-flavors are created mostly alongside Strecker degradation (Bottiroli, Aprea, Betta, Fogliano, & Gasperi, 2020;Bottiroli, Pedrotti, et al, 2020).…”

“…Milk was manufactured at industrial scale following the "in batch" production system as described in a previous work (Bottiroli, Troise, et al, 2020). The "in batch" UHLM is produced by adding the LP intended for lactose hydrolysis in a tank before UHT sterilization.…”

“…The Accela 1250 U-HPLC system (Thermo Fisher Scientific, Bremen, Germany) was interfaced to an Exactive Orbitrap HRMS (Thermo Fisher Scientific, Bremen, Germany) and the analytes were detected through a heated electrospray interface (HESI-II) operating in positive mode. Interface parameters and analytical performances were set and evaluated according to a previous work (Bottiroli, Troise, et al, 2020). Samples were spiked with 13 C-lysine before each injection and its exact mass ([M+H] + ,148.11616) was used as a reference to maximize response and to check instrumental resolution and performance.…”