Stability of ultra-high temperature treated milk: the effect of raw milk quality, storage temperature and storage time

Maria Karlsson

Stability of ultra-high temperature treated milk: the effect of raw milk quality, storage temperature and storage time

Bidragets översatta titel: Stabilitet hos mjölk med extra lång hållbarhet. Effekt av mjölkråvara, lagringstemperatur och lagringstid

Maria Karlsson

Institutionen för molekylära vetenskaper

Publikation: Avhandling › Doktorsavhandling

4 Nedladdningar

Sammanfattning

Mjölkråvarans sammansättning och egenskaper är viktiga för mjölkprodukternas stabilitet och hållbarhet, särskilt för produkter med lång hållbarhet, t.ex. ultra-hög-temperatur (UHT) behandlad mjölk. I UHT-processen värms mjölk till över 135 °C i några sekunder, vilket resulterar i en produkt med en hållbarhet på flera månader vid förvaring i rumstemperatur.I denna avhandling undersöktes hur naturliga variationer i mjölkråvarans samman-sättning och egenskaper påverkade stabiliteten hos UHT-mjölk under långtidslagring vid olika temperaturer. Under ett helt år erhölls varje månad färska prover på mjölkråvaran samt den resulterande UHT-mjölken från ett mejeri. I en experimentell studie undersöktes även effekten av att modifiera mjölkråvaran avseende nivåerna av kalcium, citrat och urea på stabiliteten hos den resulterande UHT-mjölken.Mjölkråvaran analyserades bl.a. med avseende på sammansättning, bakterier, enzymatisk aktivitet, färg och stabilitet, dvs. värmestabilitet (HCT) och alkoholtest. Under lagringen av UHT-mjölken analyserades sensoriska attribut och stabilitet. Multivariata statistiska metoder användes för att identifiera batcher av mjölk som uppvisade likheter med avseende på den totala variationen.Vi fann endast små naturliga variationer i mjölkråvaran. Modifierad råvara med mer kalcium och lägre pH hade en stark negativ effekt på UHT-mjölkens stabilitet. En mjölkråvara med högre innehåll av citrat och urea påverkade inte stabiliteten jämfört med UHT-mjölk tillverkad av icke-modifierad mjölkråvara.Lagringstemperatur korrelerade med färg och pH, medan lagringstid korrelerade med fettseparation, sedimentering och HCT. Förvaring i kyl (4 °C) eller rumstemperatur (20 °C) gav den längsta hållbarheten och begränsades av sedimentering och avvikande smak. Vid förvaring vid 30 eller 37 °C begränsades hållbarheten av flera parametrar, inklusive färg, smak och sedimentering. Förändringar i stabilitet under lagring av UHT-mjölken kunde förklaras med olika kända mekanismer.Kunskap om hur sammansättningen och egenskaperna hos mjölkråvaran påverkar stabiliteten hos den resulterande produkten kan hjälpa mejeriindustrin att förutsäga hållbarheten på UHT-mjölk. Ökad förståelse för lagringsförhållandenas betydelse för UHT-mjölkens hållbarhet kan ge konsumenter vägledning om lämplig förvaringstemperatur.

Bidragets översatta titel	Stabilitet hos mjölk med extra lång hållbarhet. Effekt av mjölkråvara, lagringstemperatur och lagringstid
Originalspråk	Engelska
Kvalifikation	Doktor i filosofi
Förlag	Swedish University of Agricultural Sciences
Tryckta ISBN	978-91-7760-454-9
Elektroniska ISBN	978-91-7760-455-6
Status	Publicerad - 2019

Nyckelord

UHT milk
colour
creaming
ethanol stability
heat coagulation time
long-term storage
raw milk
sedimentation
shelf-life

SLU-serie

Acta Universitatis Agriculturae Sueciae

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title = "Stability of ultra-high temperature treated milk: the effect of raw milk quality, storage temperature and storage time",

abstract = "The composition and properties of raw milk are important for the stability of dairy products, especially for products with long shelf-life, e.g. ultra-high temperature (UHT) treated milk. In the UHT process, milk is subjected to temperatures above 135 °C for a few seconds, resulting in a product that can be stored for several months at ambient temperature.This thesis investigated how natural variations in the composition and properties of raw milk affected the stability of UHT milk during long-term storage at different temperatures. For this purpose, samples of unprocessed raw milk as well as the resulting UHT milk were obtained every month for one year from a commercial dairy plant. Additionally, in a full factorial experiment, milk was modified with respect to levels of calcium, citrate and urea to investigate the effect on the stability of the resulting UHT milk.The quality traits analysed in the raw milk included composition, bacterial counts, enzymatic activity, colour and measures of stability, i.e. heat coagulation time (HCT) and alcohol test. During storage of UHT milk, sensory attributes and stability measures were analysed. Multivariate statistics was used to identify batches of milk showing similarities with respect to total variation.There were only small natural variations in the composition and properties of raw milk. Elevated calcium content, and associated decrease in pH, had a strong negative effect on the stability of UHT milk. Higher concentrations of citrate and urea in milk did not affect the stability compared with unmodified reference UHT milk.Storage temperature correlated with colour and pH, whereas storage time correlated with creaming, sedimentation and HCT. Cold (4 °C) or ambient (20 °C) storage gave the longest shelf-life, limited by sedimentation and deviating taste. In UHT milk stored at 30 or 37 °C, the shelf-life was limited by several parameters, including colour, taste and sedimentation. Changes in the stability of UHT milk during storage are suggested to be explained by known mechanismKnowledge of how the composition and properties of raw milk affect the stability of the resulting product can aid the dairy industry to more accurately predict the shelf-life of UHT milk. Better understanding of how storage conditions affect the shelf-life of UHT milk can provide useful guidance to consumers on appropriate storage temperature.",

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N2 - The composition and properties of raw milk are important for the stability of dairy products, especially for products with long shelf-life, e.g. ultra-high temperature (UHT) treated milk. In the UHT process, milk is subjected to temperatures above 135 °C for a few seconds, resulting in a product that can be stored for several months at ambient temperature.This thesis investigated how natural variations in the composition and properties of raw milk affected the stability of UHT milk during long-term storage at different temperatures. For this purpose, samples of unprocessed raw milk as well as the resulting UHT milk were obtained every month for one year from a commercial dairy plant. Additionally, in a full factorial experiment, milk was modified with respect to levels of calcium, citrate and urea to investigate the effect on the stability of the resulting UHT milk.The quality traits analysed in the raw milk included composition, bacterial counts, enzymatic activity, colour and measures of stability, i.e. heat coagulation time (HCT) and alcohol test. During storage of UHT milk, sensory attributes and stability measures were analysed. Multivariate statistics was used to identify batches of milk showing similarities with respect to total variation.There were only small natural variations in the composition and properties of raw milk. Elevated calcium content, and associated decrease in pH, had a strong negative effect on the stability of UHT milk. Higher concentrations of citrate and urea in milk did not affect the stability compared with unmodified reference UHT milk.Storage temperature correlated with colour and pH, whereas storage time correlated with creaming, sedimentation and HCT. Cold (4 °C) or ambient (20 °C) storage gave the longest shelf-life, limited by sedimentation and deviating taste. In UHT milk stored at 30 or 37 °C, the shelf-life was limited by several parameters, including colour, taste and sedimentation. Changes in the stability of UHT milk during storage are suggested to be explained by known mechanismKnowledge of how the composition and properties of raw milk affect the stability of the resulting product can aid the dairy industry to more accurately predict the shelf-life of UHT milk. Better understanding of how storage conditions affect the shelf-life of UHT milk can provide useful guidance to consumers on appropriate storage temperature.

AB - The composition and properties of raw milk are important for the stability of dairy products, especially for products with long shelf-life, e.g. ultra-high temperature (UHT) treated milk. In the UHT process, milk is subjected to temperatures above 135 °C for a few seconds, resulting in a product that can be stored for several months at ambient temperature.This thesis investigated how natural variations in the composition and properties of raw milk affected the stability of UHT milk during long-term storage at different temperatures. For this purpose, samples of unprocessed raw milk as well as the resulting UHT milk were obtained every month for one year from a commercial dairy plant. Additionally, in a full factorial experiment, milk was modified with respect to levels of calcium, citrate and urea to investigate the effect on the stability of the resulting UHT milk.The quality traits analysed in the raw milk included composition, bacterial counts, enzymatic activity, colour and measures of stability, i.e. heat coagulation time (HCT) and alcohol test. During storage of UHT milk, sensory attributes and stability measures were analysed. Multivariate statistics was used to identify batches of milk showing similarities with respect to total variation.There were only small natural variations in the composition and properties of raw milk. Elevated calcium content, and associated decrease in pH, had a strong negative effect on the stability of UHT milk. Higher concentrations of citrate and urea in milk did not affect the stability compared with unmodified reference UHT milk.Storage temperature correlated with colour and pH, whereas storage time correlated with creaming, sedimentation and HCT. Cold (4 °C) or ambient (20 °C) storage gave the longest shelf-life, limited by sedimentation and deviating taste. In UHT milk stored at 30 or 37 °C, the shelf-life was limited by several parameters, including colour, taste and sedimentation. Changes in the stability of UHT milk during storage are suggested to be explained by known mechanismKnowledge of how the composition and properties of raw milk affect the stability of the resulting product can aid the dairy industry to more accurately predict the shelf-life of UHT milk. Better understanding of how storage conditions affect the shelf-life of UHT milk can provide useful guidance to consumers on appropriate storage temperature.

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