The changes of physical properties in ‘Elsanta’ strawberries from the winter and summer cultivations after vibration tests

Strawberries (Fragaria x ananassa Duchesne) cv. ‘Elsanta’ were grown in the greenhouse during the winter and summer seasons of 2014 and 2015. A vibration test of strawberry fruits from these cultivations was carried out at the two frequency levels of 3 Hz and 5 Hz for 150 sec plus a control of no vibration to simulate transport. The physical properties (fruit weight, puncture, compression, electrical conductivity (EC), and respiration rate) and bruise incidence of fruits were determined after the vibration test (day 0) and after storage at 10oC (±1oC) and 70% RH (±5% RH) for 3 days (day 3). A higher average temperature (21 as opposed 25oC) during strawberry growth and development of the summer crop gave a shorter period for harvesting, with a smaller fruit and a softer fruit as compared to a lower average temperature in the winter cultivation (8 to 21oC). The fruit from the summer cultivation when vibrated at a frequency of 5 Hz were observed to have significantly higher for wet bruise (50% of total fruits), electrical conductivity (EC) and respiration rate (63.78 mgCO2/kg.hr), as well as lower firmness values (puncture and compression tests) than other treatments (p≤0.05). The lower vibration level at 3 Hz of the winter strawberries did not affect the percentage of bruise and both firmness values (p>0.05), whilst the EC method could noticeably distinguish the bruise incidence, particularly for a frequency of 5 Hz (p≤0.05). The EC method gave a highly significant correlation with wet bruise (r = 0.854) and severity score (r = -0.499) when compared with either firmness tests (puncture and compression) or respiration rate (p≤0.01). The EC technique is suggested for use as a bruise indicator of strawberries and an application for a bruise assessment for a whole strawberry punnet during postharvest handling operation and transport.