Main conclusions

• The freezing time was reduced by 19.9 % in US-treated samples. 
• There were no differences in the water-holding capacity and cook-loss after thawing in US-treated samples and non-treated samples. 

Background

US is a technology that produces microvibrations in the medium in which it is applied, promoting mass and energy-transfer processes. Normally, it is applied in liquid media or solid products immersed in liquid media to favour the cavitation phenomenon. However, there are very few studies concerning US application by direct contact with the food without the use of a liquid medium. 

Purpose of the study

The purpose of this study was to evaluate the application of direct-contact US during the freezing of chicken samples and its effect on the freezing rates and quality of the frozen products. 

Methods

Trial conditions:

• Sample: chicken 
• US treatment: net sonication time of 37 % (3 s on / 5 s off throughout freezing). 
• Freezing conditions: freezing tunnel; air temperature -15 °C; air speed <0.4 m/s. 
• Thawing conditions: cold room at 4 °C. 
• Water-Holding Capacity (WHC): 5–6 g samples were prepared and wrapped in a gauze and placed in a Falcon tube with glass pearls. These tubes were centrifuged at 1300 rpm for 15 minutes. WHC = 100 - weight loss (%) 
• Cook-loss (CL): samples of 2 g were weighed and placed in test tubes and immersed in boiling water until a final sample temperature of 75 °C was reached at the thermal centre. CL = weight loss (%) 

What was investigated

Freezing time

By applying US during freezing, the processing time was reduced by 19.9 %. 

Water-Holding Capacity (WHC) 

No differences were observed in WHC after the thawing of chicken samples frozen with US and of samples frozen without US, presenting values between 80-85 %. 

Cook-loss (CL) 

No differences were observed in CL after the thawing of chicken samples frozen with US and of samples frozen without US, presenting values between 10-15 %.