1H NMR spectroscopy has proved to be a valuable research tool in the field
of food science and technology, especially in the case of food lipids. It is well known
that degradation processes affecting food lipids during technological processing and
storage can be a major cause of food deterioration, with negative implications from the
economic and health point of view. Although classical methodologies based on long,
multi-step, tedious and unspecific techniques are widely employed, a large number of
studies have demonstrated the usefulness of 1H NMR in not only characterizing
qualitatively and quantitatively major and minor lipidic components of foods, oils and
fats, but also when studying their degradation process under different oxidative
conditions, helping to shed light on the underlying mechanisms by which lipid
degradation occurs.
Nevertheless, the nutritional quality and safety of lipids could also be modified during
subsequent human gastrointestinal digestion. Since this physiological process is an
inevitable step, it seems logical also to research the various chemical reactions that may
affect food lipidic components under gastrointestinal digestive conditions, in order to
better understand the effect of lipids on human health and also to be able to design
healthier foods and diets. Recent studies along these lines have demonstrated the
suitability of 1H NMR for simple, fast and accurate global study of lipolysis, without
chemical modification of the sample. This new methodology overcomes many of the
limitations of the techniques currently used for this purpose. In addition, by using
spectral data and applying different approaches, 1H NMR is a valuable alternative for
the quantification of the various kinds of glyceryl structures and fatty acids in a simple,
fast and accurate way in complex lipid mixtures.
Beside lipolysis, other chemical reactions affecting lipids, such as oxidation, might also
take place in the gastrointestinal tract due to its highly reactive environment. However,
given the small number of studies and the limitations of the methodologies usually
employed (absorbance in the ultraviolet visible region for determining conjugated
dienes, peroxide value, thiobarbituric acid reactive substances test), there is currently knowledge lacking about the extent of ongoing chemical reactions, especially of lipid
oxidation, as well as about the specific nature of the oxidation products generated from
lipids that could remain bioaccessible for intestinal absorption. It must be noted that 1H
NMR allows, in the same run, a study not only of the above-mentioned lipolysis
reaction, but also that of the occurrence and extent of oxidation reactions taking place
during digestion. This technique provides valuable knowledge about oxidation products
generated from polyunsaturated lipids under these conditions. It has been observed that
both the amount and the nature of lipid oxidation products vary widely, depending on
the unsaturation degree and the initial oxidation level of the digested lipids, as well as
on the presence of other non-lipidic components that are usually present in food, like
proteins or antioxidants. The information provided by 1H NMR allows the
simultaneous study of a broad variety of oxidation products, which is crucial for the
selection of the most useful marker compounds of the occurrence and extent of lipid
oxidation. Likewise, 1H NMR facilitates the study of the bioaccessibility of certain
minor lipidic compounds of interest, which is another important aspect of food
digestion research that is difficult to tackle. All these matters will be dealt with in this
chapter.
Keywords: Antioxidants, Bioaccessibility, Degradation process, Food science
and technology, Lipid digestion research, Lipolysis, 1H NMR spectroscopy.