Freshness and sensory quality of packaged wild rocket

Sensory descriptive analysis was used to evaluate visual and overall freshness and the underlying attributes of freshness of packaged wild rocket (Diplotaxis tenuifolia L.) quality. Variation was induced by differences in package atmosphere, temperature and storage time. The leaves were packaged in trays wrapped in film with a low oxygen transmission rate (OTR) (low OTR; 0.65 pmol s−1 m−2 kPa−1) or high OTR (high OTR; 17.4 pmol s−1 m−2 kPa−1). To create packages with variation in O2 and CO2 concentrations in the package atmosphere, and in the sensory quality, the packages were stored at 2 °C for 6 or 7 d or at elevated temperatures (10, and 20 °C) for various times (2, 3, 4, and 6 d). At low OTR, the O2 concentration decreased to ≤0.5 kPa, and the leaves developed a ‘smoked odor’, lost leaf integrity and texture, and turned olive-brown. At high OTR, the O2 concentrations inside the package remained at 10–18 kPa, and leaves showed signs of senescence, i.e. light-green to yellow leaves and a heterogeneous appearance of leaves in the tray. Freshness of the leaves was evaluated by sensory analysis without prior consensus. ‘Visual freshness’ was evaluated at first sight before opening the packages, while ‘overall freshness’ was evaluated after opening and careful inspection by looking, smelling and touching the product. ‘Visual freshness’ was highly correlated to green leaf color (r = 0.98), whereas ‘overall freshness’ was described by color, odor and texture as found by interval PLS. The high OTR packages had similar scores for ‘freshness’ before and after opening (P > 0.05), while the low OTR packages had significantly different scores (P ≤ 0.05). As appearance is an indication of freshness at purchase, wild rocket must be MAP packaged in an OTR film that permits sufficient levels of O2 for aerobic respiration when storage temperature cannot be controlled and kept low during distribution and retail.

► Evaluation of ‘visual freshness’ of wild rocket relies on green color, while ‘overall freshness’ relies on color, odor and texture if MAP is used.
► Scores for freshness of MAP wild rocket are similar before and after opening of the packages, if O2 is maintained at high levels (≥10 kPa) during storage.
► At high temperatures (20 °C), high OTR film must be used to meet consumers’ expectations for quality at purchase.
► Accumulated temperature during storage cannot be used alone to model changes in ‘visual’ and ‘overall freshness’.