Search

Industrial fruit products were investigated for their content of pectin methylesterase (PME) residual activity by a new procedure that allows selective concentration by affinity chromatography of the active form of the enzyme, when present. The technique utilizes a protein inhibitor, purified from kiwifruit, covalently bound to a Sepharose resin. This inhibitor, in fact, binds with high affinity the native active form of PME that can be subsequently recovered by dissociating the complex at alkaline pH with high ionic strength. In this way the enzyme is recovered at a concentration suitable for pH-stat assay. We examined fruit products from several industrial preparations of peach, pear, apple, apricot and pineapple. The analysed fruit purees showed PME activities between 10 ‐3 and 10 ‐5 U/mL, whereas the nectars did not show any detectable activity although cloud loss phenomenon was often observed. The diced fruit samples showed activities between 10 ‐2 and 10 ‐5 U/g. The highest values were found in samples of chi grape (10 ‐2 U/g) and pineapple (10 ‐3 U/g). A dependence of the intensity of cloud loss on the levels of PME residual activity was found.

BACKGROUND The so-called 'Neapolitan limmo' or 'lemoncetta Locrese' is an old and now rare Mediterranean sweet lime, similar to lemon but smaller. It is a fruit distinguished from orange, lemon, mandarin, and lime for its sweeter, watery, and non-acidic taste, with a pH between 5.6 and 5.9. No compositional studies are currently available for this citrus fruit. Here we report, for the first time, the distribution in the limmo juice of free amino acids and their main derivatives such as betaines and related ammonium compounds. RESULTS Seven proteinogenic amino acids (proline, asparagine, serine, aspartic acid, glutamine, alanine, and threonine) and a non-protein amino acid (γ-aminobutyric acid) characterize Neapolitan limmo juice. Proline betaine is the predominant betaine. The data were compared with those of other important citrus juices. CONCLUSION The specific 'taste quality' of Neapolitan limmo juice can be attributed to its peculiar composition in amino acids. The species-specific presence of the ammonium compound derivatives of the amino acid proline, with proline betaine as the predominant betaine, characterize the non-acidic varieties of Mediterranean sweet lime. Our study constitutes an important step towards the repopulation of this ancient plant and its exploitation in food industry. © 2020 Society of Chemical Industry.

Pigments, such as carotenes, xanthophylls and chlorophylls, were extracted from both vegetables and their industrial products by using a 2:1 (v/v) dichloromethane/methanol solution. To separate and quantify the components in the extraction mixture, a HPLC analysis on reversed phase C30 column and binary gradient, made of methanol/water solution and dichloromethane, was employed. This gradient appears to have some advantages over other reported methods, which utilize reversed phase C30 column, in terms of resolution and analysis time. The linearity range of the detection response, the chromatographic resolution of a standard mixture constituted of lutein, zeaxanthin, trans-s-apo-8?-carotenal, s-cryptoxanthin, chlorophyll-b, ?-carotene, chlorophyll-a, ?-carotene, lycopene and the conditions for the complete extraction of those substances from the vegetable matrix were investigated. Both retention time and peak area reproducibility showed an average variation coefficient of about 2% for all the analyzed comp...

The thermal stability of three forms of pectin methylesterase purified from tomato was evaluated at pH 4.5. The time-dependent heat-inactivation curves for the three forms exhibit exponential behaviour in the temperature range between 70 °C and 90 °C. The determination of DT and Z parameters displays a different heat-inactivation kinetic among the three isoenzymes. In particular, two forms (PME1 and PME3) show similar behaviour with a Z value of 24 °C, whereas the third form (PME2) shows a Z value of 15 °C.

The chemical composition of 30 samples of juices obtained from bergamot (Citrus bergamia Risso and Poit.) fruits is reported and compared to the genuineness parameters adopted by Association of the Industry of Juice and Nectars (AIJN) for lemon juice. It was found that the compositional differences between the two juices are distinguishable, although with difficulty. However, these differences are not strong enough to detect the fraudulent addition of bergamot juice to lemon juice. Instead, we found the high-performance liquid chromatography (HPLC) analysis of the flavanones naringin, neohesperidin, and neoeriocitrin, which are present in bergamot juice and practically absent in the lemon juice, is a convenient way to detect and quantify the fraudulent addition of bergamot juice. The method has been validated by calculating the detection and quantification limits according to Eurachem procedures. Employing neoeriocitrin (detection limit = 0.7 mg/L) and naringin (detection limit = 1 mg/L) as markers, it is possible to detect the addition of bergamot juice to lemon juice at the 1% level. When using neohesperidin as a marker (detection limit = 1 mg/L), the minimal percentage of detectable addition of bergamot juice was about 2%. Finally, it is reported that the pattern of flavonoid content of the bergamot juice is similar to those of chinotto (Citrus myrtifolia Raf) and bitter orange (Citrus aurantium L.) juices and that it is possible to distinguish the three kinds of juices by HPLC analysis.

A new extraction and chromatographic procedure to quantify free and esterified ergosterol in tomato products was devised. The extraction solution was composed of a dichloromethane/methanol mixture in a 2:1 (v/v) ratio. This extraction solvent allowed for higher ergosterol recovery from tomato products (an average of 25% more) compared to hexane, which is frequently employed for ergosterol extraction. Both free and esterified ergosterol were determined by HPLC reverse-phase chromatography employing a Nova-Pak C-18 column (300 x 3.9 mm), filled with 4 mm average particle size and a guard column of the same material. The elution was performed at a flow rate of 1 mL. min(-1) with a linear gradient of solvent A (methanol/water, 80:20, v/v) and solvent B (dichloromethane). The gradient, starting at sample injection, was from 0 to 50% B for 20 min for the free ergosterol analysis and additional 15 min at 50% B to analyze the ergosterol esters. This technique has proven to be more sensitive for ergosterol determination than other reported chromatographic procedures. Moreover, ergosterol esters, extracted from various fungal sources, separated well and were easily quantified.