Quantitation of total vitamin D2 and D4 in UV-exposed mushrooms using HPLC with UV detection after novel two-step solid phase extraction

A robust method for quantitation of total vitamin D2 and D4 in mushrooms by high performance liquid chromatography with UV detection (HPLC-UV) was developed to analyze mushrooms exposed to UV light. A two-step solid phase extraction (SPE) (silica, carbon black) removed chromatographic interferences typically resolved only with mass spectrometric detection (LC-MS) and allowed quantitation of all vitamin D and pre-D analytes. The vitamin and pre-vitamin forms of D2, D4 and D3 (internal standard), as well as other photoisomers and sterols were resolved. Results for six types of UV-exposed mushrooms were comparable to LC-MS. Screening of ten additional types of UV-exposed mushrooms without the IS confirmed lack of interference with the IS. The limit of quantification (µg/100 g fresh weight) was 0.4 for vitamin D and 0.9 for pre-vitamin D. Mushrooms do not have to be dried, and separatory funnels and large solvent volumes were also eliminated from sample preparation.

Dietary fiber, starch, and sugars in bananas at different stages of ripeness in the retail market

The goal of this work was to evaluate changes in dietary fiber measured by the traditional enzymatic-gravimetric method (AOAC 991.43) and the more recently accepted modified enzymatic-gravimetric method (AOAC 2011.25), mono- and disaccharides, and starch as a function of assessed ripeness in a controlled study of a single lot of bananas and in bananas at the same assessed stages of ripeness from bananas purchased in retail stores, from different suppliers. Sugars, starch, and dietary fiber were analyzed in bananas from a single lot, at different stages of ripeness, and in retail samples at the same assessed stages of ripeness. Mean fiber measured by the traditional enzymatic-gravimetric method (EG) was ~2 g/100g and not affected by ripeness. Mean fiber assessed with the recently modified method (mEG) was ~18 g/100g in unripe fruit and decreased to 4-5 g/100g in ripe and ~2 g/100g in overripe bananas. Slightly ripe and ripe bananas differed by ~1.1 g/100g in the controlled single-lot study but not among retail samples. There was a large increase in fructose, glucose and total sugar going from unripe to ripe with no differences between ripe and overripe. Aside from stage of ripeness, the carbohydrate composition in retail bananas is likely affected by differences in cultivar and post-harvest handling. Results from this study demonstrate the importance of measuring dietary fiber using the mEG approach, developing more comprehensive and sensitive carbohydrate analytical protocols and food composition data, and recognizing the impact of different stages of maturity and ripeness on carbohydrate intake estimated from food composition data.

Seasonal variability of the vitamin C content of fresh fruits and vegetables in a local retail market

BACKGROUND

Seasonal variation of vitamin C in fresh fruits and vegetables is not reflected in food composition database average values, yet many factors influence content and retention.

RESULTS

Fresh fruits and vegetables were sampled on three occasions in each season, from the same local retail outlets, for 1 or 2 years. Vitamin C was significantly higher in winter-sampled spinach (436 mg kg^-1 ) compared with spring (298 mg kg^-1 ) and summer/fall (180 mg kg^-1 ); in potatoes in summer/fall (156 mg kg^-1 ) versus winter/spring (106 mg kg^-1 ); and in oranges in winter (616 mg kg^-1 ), spring (592 mg kg^-1 ), and summer (506 mg kg^-1 ). Ranges were dramatic among sampling occasions for broccoli, oranges, potatoes, and spinach (700-1210 mg kg^-1 , 420-780 mg kg^-1 , 70-280 mg kg^-1 , and 90-660 mg kg^-1 respectively). Mean values for apples, bananas, tomatoes, and potatoes differed from the USDA National Nutrient Database for Standard Reference (SR) average by ≥10% of the daily recommended intake (90 mg). For broccoli, oranges, and spinach, vitamin C was substantially above or below the SR range in 50-100% of the samples. For spinach, the average content did not differ from SR, but vitamin C in winter was 55% higher than SR.

CONCLUSION

Database average values for vitamin C in fresh produce can significantly over- or underestimate the content in a specific food supply. © 2018 Society of Chemical Industry.