# Chemical and physical analysis

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Measurements that connect cultivation treatments to plant chemistry, volatile compounds, soluble solids, acidity, colour and texture.

In brief

Measurements that connect cultivation treatments to plant chemistry, volatile compounds, soluble solids, acidity, colour and texture.

## Measurement chain

 |
 Outcome | Preferred method | interpretation

 | Volatile profile | HS-SPME GC–MS with internal standard and batch QC | chemical abundance is not identical to perceived aroma
 | Phenolics/target metabolites | validated HPLC/LC method | target list and extraction recovery reported
 | Mineral composition | ICP-OES/ICP-MS or validated equivalent | dry/fresh mass basis stated
 | Soluble solids | refractometry, °Brix | not universally equal to perceived sweetness
 | Titratable acidity | standardised titration | more informative than tissue pH alone for acid load
 | Colour | calibrated L*a*b* imaging or colorimetry | illumination and calibration controlled
 | Texture | instrumental compression/puncture plus sensory descriptor | method geometry and speed reported
 | Fresh/dry mass | traceable balance and drying method | concentration and total amount both reported

Instrumental colour may be reported in CIE L*a*b* coordinates when acquisition, illuminant, observer, instrument geometry and calibration are fixed. [R45]

## Sampling control

Plant position, leaf age, time of day, harvest-to-analysis delay, storage temperature and sample preparation are standardised. Lettuce research shows that nutrient solution, season and post-harvest handling can alter quality and shelf-life interpretation. [R26]

## Reporting concentration correctly

A treatment may increase a compound per gram while reducing total biomass. Report both concentration and total content per plant where feasible.

## References

- [R26] Luna, María C.; Martínez-Sánchez, Ascensión; Selma, María V.; Tudela, Juan A.; Baixauli, Carlos; Gil, María I. (2013). Influence of nutrient solutions in an open-field soilless system on the quality characteristics and shelf life of fresh-cut red and green lettuces (Lactuca sativa L.) in different seasons. *Journal of the Science of Food and Agriculture*. https://doi.org/10.1002/jsfa.5777
- [R45] International Organization for Standardization; International Commission on Illumination (2019). ISO/CIE 11664-4:2019 Colorimetry — Part 4: CIE 1976 L*a*b* colour space. *International Standard*.