Page 75 - FoodFocusThailand No.245 September 2026

Effects on Nutritional Value A key characteristic of ESL milk is its fresh-like sensory
Thermal processing can induce changes in various milk quality, including a naturally white appearance, fresh milk
components, including proteins, sugars, vitamins, and bioactive aroma, clean flavor, characteristic milkiness, creaminess, and
compounds. The extent of these changes depends on the a smooth texture comparable to those of pasteurized milk.
processing temperature, duration of heat exposure, method These sensory attributes result from the combined effects of
of heat transfer, and storage conditions. Therefore, when protein structure, fat globule distribution, volatile compound
evaluating the effects of ESL processing on nutritional value, composition, and the minimization of changes induced by
the overall thermal load should be considered rather than thermal processing or product deterioration. Consequently,
focusing solely on the maximum temperature applied during ESL technologies that reduce the overall thermal load,
processing.² such as microfiltration, bactofugation, and rapid heat
Key indicators commonly used to assess the effects of treatment, tend to preserve fresh-like characteristics more
heat treatment in milk include lactulose and furosine, both effectively than processes relying solely on severe heat
of which tend to increase with increasing severity of thermal treatment.
processing and may continue to increase during storage.¹² In Aroma and flavor are major determinants of consumer
general, pasteurized milk contains the lowest levels of these preference. Heat treatment causes the denaturation of whey
heat-treatment indicators, whereas UHT milk exhibits higher proteins, particularly β-lactoglobulin, leading to the exposure
levels. In ESL milk, their concentrations vary depending on the and release of sulfhydryl groups and the formation of volatile
processing technology and conditions employed and generally sulfur compounds, such as hydrogen sulfide, methanethiol,
fall between those observed in pasteurized and UHT milk. and dimethyl sulfide, which are associated with boiled and
Heat treatment also promotes the Maillard reaction, which cooked flavors. In addition, lipid oxidation and the Maillard
can affect the color and flavor of milk and may reduce the reaction generate volatile compounds that can shift the
nutritional availability of certain amino acids, particularly lysine. sensory profile from a fresh flavor toward a cooked flavor. The
These changes become more pronounced when milk is exposed extent of these changes depends on processing temperature,
to more severe heat treatment or prolonged storage. However, duration of heat exposure, method of heat treatment, and
in ESL milk subjected to a low-to-moderate thermal load, such subsequent changes occurring during storage. 15
effects are generally limited compared with those observed in Texture is influenced by changes in casein micelles,
UHT milk. Furthermore, furosine levels in commercial ESL milk whey protein aggregation, and fat globule distribution, all
may vary considerably depending on the processing conditions of which affect product viscosity, creaminess, and stability.
employed. Therefore, the term “ESL” alone should not be used Excessive protein aggregation may increase viscosity or
as an indicator of the extent of heat-induced changes; instead, lead to sediment formation, whereas the activity of microbial
appropriate heat-treatment indicators should be evaluated enzymes may contribute to bitterness and reduced product
in conjunction with information on the specific processing stability. Therefore, monitoring viscosity, sedimentation,
conditions.² bitterness, and overall acceptability is important when
Regarding vitamins, their thermal stability varies considerably evaluating the shelf life of ESL milk.
among different types. Certain water-soluble vitamins are more Sensory quality assessment should involve both trained
susceptible to heat, oxygen, and light than fat-soluble vitamins. panelists and target consumers. A trained descriptive panel
However, vitamin losses associated with milk processing can monitor changes in sensory attributes such as fresh
generally do not result in a significant change in the overall milk aroma, cooked flavor, oxidized flavor, creaminess,
nutritional value of milk.¹³ Therefore, nutritional quality should bitterness, and aftertaste, whereas consumer testing
be evaluated on the basis of the overall nutrient composition, provides direct information on product liking and purchase
rather than focusing solely on changes in any individual vitamin. intention. Applicable sensory methods include Quantitative
Regarding minerals, such as calcium, phosphorus, Descriptive Analysis (QDA), Check-All-That-Apply (CATA),
magnesium, and potassium, these nutrients are not directly Rate-All-That-Apply (RATA), and acceptability/rejection tests.
destroyed by heat treatment. However, thermal processing For determining sensory shelf life, survival analysis can be
may alter the equilibrium of minerals in the serum phase and used to estimate the time at which a predefined proportion of
the distribution of calcium phosphate associated with casein consumers rejects the product. This approach is particularly
micelles. suitable for products that undergo gradual changes in
In summary, the nutritional advantage of ESL milk does not sensory quality during storage. 16
imply that it contains higher levels of nutrients than other In summary, high-quality ESL milk should retain fresh
types of milk. Rather, it arises from the use of processing aroma and fresh flavor characteristics comparable to those
conditions that minimize the overall thermal load and limit of pasteurized milk, with minimal cooked and oxidized flavors,
changes in heat-sensitive components. Consequently, ESL while maintaining consistent color, creaminess, and texture
processing can help preserve protein structure and maintain throughout its shelf life. However, consumer acceptance is
the nutritional quality of milk as close as possible to that of also influenced by factors such as familiarity, consumption
pasteurized milk.² culture, the type and level of milk fat, and product-related
information. Therefore, the success of ESL milk should not
Sensory Quality and Consumer Acceptance be evaluated solely on the basis of achieving the longest
Sensory quality is a key factor influencing consumer acceptance possible shelf life, but rather by the length of time during
and determining the shelf life of ESL milk, as consumers perceive which the product remains safe, maintains its quality, and
product quality through attributes such as color, aroma, flavor, is acceptable to consumers under actual storage and
texture, and freshness. Even when a product continues to distribution conditions.
meet microbiological criteria, the development of cooked flavor,
oxidized flavor, bitterness, or undesirable changes in texture
may lead to consumer rejection before the microbiological end
point of shelf life is reached. Therefore, shelf-life determination
should incorporate sensory quality assessment together with More Information Service Info C013
microbiological, physical, and chemical data. 14
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