Analytical Methods for Extraction and Identification of Primary and Secondary Metabolites of Apple (Malus domestica) Fruits: A Review

Abstract

Apples represent a greater proportion of the worldwide fruit supply, due to their availability on the market and to the high number of existing cultivar varieties and apple-based products (fresh fruit, fruit juice, cider and crushed apples). Several studies on apple fruit metabolites are available, with most of them focusing on their healthy properties’ evaluation. In general, the metabolic profile of apple fruits strongly correlates with most of their peculiar characteristics, such as taste, flavor and color. At the same time, many bioactive molecules could be identified as markers of a specific apple variety. Therefore, a complete description of the analytical protocols commonly used for apple metabolites’ characterization and quantification could be useful for researchers involved in the identification of new phytochemical compounds from different apple varieties. This review describes the analytical methods published in the last ten years, in order to analyze the most important primary and secondary metabolites of Malus domestica fruits. In detail, this review gives an account of the spectrophotometric, chromatographic and mass spectrometric methods. A discussion on the quantitative and qualitative analytical shortcomings for the identification of sugars, fatty acids, polyphenols, organic acids, carotenoids and terpenes found in apple fruits is reported.

Analysis of Fatty Acids, Amino Acids and Volatile Profile of Apple By-Products by Gas Chromatography-Mass Spectrometry

“…Considering the above, we can assess that the extraction procedure, method used for analysis, pedo-climatic conditions, genetic factors, and apple maturity stage are the main factors that could influence the fatty acid by-product total amount. For instance, fatty acids could be extracted with different solvents such as hexane or petroleum ether and be further analyzed through GC-FID (gas chromatography coupled with flame ionization detector) or GC-MS (gas chromatography coupled with mass spectrometry) [ 17 ].…”

“…Golden Delicious apples are preferred by consumers mainly because of their sweetness, color, firmness, intensive flavor, and light crunchiness [ 16 ]. They were characterized by Acquavia et al [ 17 ] as having a golden yellow color, a crunchy and juicy pulp with a very sweet flavor being mainly used for juice, cider, jams, and canned goods manufacturing, having, as a substantial disadvantage, compared with other varieties, thin skin. Due to this drawback, they have a significant tendency to dehydration and more attention should be paid to their storage [ 18 ].…”

Arnica montana Cell Culture Establishment, and Assessment of Its Cytotoxic, Antibacterial, α-Amylase Inhibitor, and Antioxidant In Vitro Bioactivities

“…Quantification of Phenolic Compounds and Sesquiterpene Lactones TPC, TFC, and TPAC were determined according to Vazquez-Marquez et al [66]. These spectrophotometric methods are common in phytochemical analysis to determine the content of secondary metabolites based on the use of reference standards for comparison [67][68][69]. For TPC, a gallic acid standard (Sigma-Aldrich, St. Louis, MO, USA) was used to prepare solutions at concentrations from 6 to 100 µg/mL to build the calibration curve (y = 8.2506x -0.0048, R 2 = 0.9995).…”

HRMS Characterization, Antioxidant and Cytotoxic Activities of Polyphenols in Malus domestica Cultivars from Costa Rica

“…However, despite increased research efforts, existing information is insufficient for most of the dietary sources of polyphenols, hence the growing trend in the consumption of dietary supplements derived from these compounds, which increases the need for accurate and up-to-date information about their chemical and bioactive properties. A significant number of publications are available that indicate that apples have antioxidant activity, and for instance that they inhibit the growth of cancer cells among other health benefits, and many of them attribute these effects to their polyphenols [ 13 , 15 , 16 ].…”

“…Different studies have presented evidence for the diversity of chemical components based on locations and cultivars [ 13 , 16 , 17 , 18 ]. Differences in phytochemical composition between apple cultivars are influenced by biotic interactions and show that important characteristics such as microbiome composition are dependent on geographical location and local environment [ 19 , 20 ].…”