Application of carbon and hydrogen stable isotope analyses to detect exogenous citric acid in Japanese apricot liqueur

Effect of water deficit stress during fruit cultivation on the carbon stable isotopes of organic acids in Japanese apricots and liqueur prepared from these fruits

ABSTRACTThe objective of this study was to assess the impact of water deficit stress during fruit cultivation on the δ13C values of citric acid and malic acid in Japanese apricots at different ripeness stages and their resulting liqueurs. Our experiments show that water deficit stress increases the δ13C values of citric acid and malic acid in tree-ripened fruits, counteracting the typical decrease during ripening. However, water deficit treatment has a minimal effect on the δ13C values of organic acids in green fruits. Regardless of fruit ripeness or water status, the δ13C values of organic acids in fruits are directly reflected in the resulting liqueurs. Overall, water deficit stress during fruit cultivation has the potential to promote similarity in the δ13C values of organic acids across fruits at different ripeness levels, reducing variations among liqueurs derived from fruits of varying ripeness levels.

Natural complex substances: From molecules to the molecular complexes. Analytical and technological advances for their definition and differentiation from the corresponding synthetic substances

Natural complex substances (NCSs) are a heterogeneous family of substances that are notably used as ingredients in several products classified as food supplements, medical devices, cosmetics and traditional medicines, according to the correspondent regulatory framework. The compositions of NCSs vary widely and hundreds to thousands of compounds can be present at the same time. A key concept is that NCSs are much more than the simple sum of the compounds that constitute them, in fact some emerging phenomena are the result of the supramolecular interaction of the constituents of the system. Therefore, close attention should be paid to produce and characterize these systems. Today many natural compounds are produced by chemical synthesis and are intentionally added to NCSs, or to formulated natural products, to enhance their properties, lowering their production costs. Market analysis shows a tendency of people to use products made with NCSs and, currently, products made with ingredients of natural origin only are not conveniently distinguishable from those containing compounds of synthetic origin. Furthermore, the uncertainty of the current European regulatory framework does not allow consumers to correctly differentiate and identify products containing only ingredients of natural origin. The high demand for specific and effective NCSs and their high-cost offer on the market, create the conditions to economically motivated sophistications, characterized by the addition of a cheap material to a more expensive one, just to increase profit. This type of practice can concern both the addition of less valuable natural materials and the addition of pure artificial compounds with the same structure as those naturally present. In this scenario, it becomes essential for producers of natural products to have advanced analytical techniques to evaluate the effective naturalness of NCSs. In fact, synthetically obtained compounds are not identical to their naturally occurring counterparts, due to the isotopic composition or chirality, as well as the presence of different trace metabolites (since pure substances in nature do not exist). For this reason, in this review, the main analytical tests that can be performed to differentiate natural compounds from their synthetic counterparts will be highlighted and the main analytical technologies will be described. At the same time, the main fingerprint techniques useful for characterizing the complexity of the NCSs, also allowing their identification and quali-quantitative evaluation, will be described. Furthermore, NCSs can be produced through different manufacturing processes, not all of which are on the same level of quality. In this review the most suitable technologies for green processes that operate according to physical extraction principles will be presented, as according to the authors they are the ones that come closest to creating more life-cycle compatible NCSs and that are well suited to the European green deal, a strategy with the aim of transforming the EU into a sustainable and resource-efficient society by 2050.

Prediction method for determining the carbon stable isotopic composition of berry sugars in the original must of Chardonnay wines

The carbon stable isotopic composition, as indicated by the δ¹³C value, of wine ethanol is inherited from berry sugars, but little is known about the variation in sugar δ¹³C values of Japanese grapes relative to overseas grapes. This study found a large variation in sugar δ¹³C values of Chardonnay grapes grown in Japan (-27.2 ± 0.9‰, mean ± standard deviation, n = 33), with sugar δ¹³C values depending on the δ¹³C values and content of monosaccharides. After complete fermentation, the carbon isotope discrimination between berry sugars and wine ethanol was 1.5 ± 0.1‰. Ethanol δ¹³C values and carbon isotope discrimination enabled prediction of sugar δ¹³C values in the original must. Imported wines had higher sugar δ¹³C values than those of wines made from Japanese grapes, suggesting drier overseas viticulture conditions. The determination of sugar δ¹³C values in grape berries provides valuable information for viticulture and wine authentication.

Discrimination for sake brewing methods by compound specific isotope analysis and formation mechanism of organic acids in sake

Organic acids in sake affect its aroma and color and help control the activity of microorganisms. This study used liquid chromatography coupled with isotope ratio mass spectrometry and solid-phase extraction to determine the stable carbon isotope ratios (δ¹³C) for malic acid, lactic acid, and succinic acid in 49 sake samples. The mean δ¹³C of lactic acid was -25.6 ± 2.1‰ in kimoto samples and -20.2 ± 2.5‰ in sokujo sample. According to linear discriminant analysis using δ¹³C of lactic acid, 87.8% of kimoto and sokujo samples were correctly identified. The proportion of brewers' lactic acid in sake could be calculated from the δ¹³C value of lactic acid for the first time. The productions of malic acid and succinic acid may be conducted by some kinds of fermentation and the mechanism of the tricarboxylic acid cycle by using δ¹³C of malic acid and succinic acid.

Assessing the authenticity of animal rennet using δ15N analysis of chymosin

Chymosin is a protease that curdles the milk casein. Animal rennet was the first discovered source of chymosin and its use is mandatory for the production of PDO cheeses such as Parmigiano Reggiano and Grana Padano. Of the alternatives, fermentation-produced chymosin is the most competitive because it functions in a similar way, but is much cheaper. Analytical tools are necessary in order to distinguish the 2 types of chymosin and verify the compulsory use of animal rennet in the production of PDO cheeses. In this work, a method to analyse ¹⁵N/¹⁴N in chymosin after extraction was developed. The δ¹⁵N values of animal rennet range from 5.7‰ to 8‰, whereas the δ¹⁵N values of fermentation-produced chymosin are significantly lower, ranging from -5.3‰ to 2.2‰. A threshold value of 5.7‰ was defined for authentic animal rennet. Addition of fermentation-produced chymosin to animal rennet, or its complete substitution, can be therefore detected.

Carbon stable isotopic compositions of citric acid and malic acid in Japanese apricot liqueur decrease as the fruit ripens

The carbon stable isotopic composition (δ¹³C) is often analyzed to quantify the addition of acidulants to Japanese apricot liqueur, but little is known about the variation in the δ¹³C values of the main organic acids arising from differences in the ripeness of Japanese apricots. We show that in Japanese apricot liqueur prepared using fruits at different stages of ripeness, the δ¹³C values of citric acid and malic acid ranged from -25.1‰ to -23.7‰ and from -22.3‰ to -19.7‰, respectively, and the δ¹³C values decreased as the fruit ripened. The average δ¹³C value of citric acid from liqueurs was 0.7‰ higher than that from fresh fruits, whereas the δ¹³C values of malic acid showed no isotope discrimination. The variation in δ¹³C values of the main organic acids in Japanese apricot liqueurs will help detect acidulant addition and control authenticity.