Quantitative methods to measure pigmentation variation in farmed Giant Tiger Prawns, Penaeus monodon, and the effects of different harvest methods on cooked colour

Abstract

Cooked prawn colour is known to be a driver of market price and a visual indicator of product quality for the consumer. Although there is a general understanding that colour variation exists in farmed prawns, there has been no attempt to quantify this variation or identify where this variation is most prevalent. The objectives of this study were threefold: firstly to compare three different quantitative methods to measure prawn colour or pigmentation, two different colorimeters and colour quantification from digital images. Secondly, to quantify the amount of pigmentation variation that exists in farmed prawns within ponds, across ponds and across farms. Lastly, to assess the effects of ice storage or freeze-thawing of raw product prior to cooking. Each method was able to detect quantitative differences in prawn colour, although conversion of image based quantification of prawn colour from RGB to Lab was unreliable. Considerable colour variation was observed between prawns from different ponds and different farms, and this variation potentially affects product value. Different post-harvest methods prior to cooking were also shown to have a profound detrimental effect on prawn colour. Both long periods of ice storage and freeze thawing of raw product was detrimental to prawn colour. However, ice storage immediately after cooking was shown to be beneficial to prawn colour. Results demonstrated that darker prawn colour was preserved by holding harvested prawns live in chilled seawater, limiting the time between harvesting and cooking, and avoiding long periods of ice storage or freeze thawing of uncooked product.

Dietary astaxanthin levels affect colour, growth, carotenoid digestibility and the accumulation of specific carotenoid esters in the Giant Tiger Shrimp,Penaeus monodon

“…Although not the focus of this study, shrimp fed different amounts of dietary carotenoid for 6 weeks showed significant colour differences ( Fig. S1), as quantified from uncooked shrimp colour using digital images using established methods (Wade, Paulo, Goodall, Fischer, Poole & Glencross 2014).…”

Reflected‐light Influences the Coloration of the Peppermint Shrimp, Lysmata boggessi (Decapoda: Caridea)

“…The digital image analysis was previously used in other crustaceans, that is, clawed lobsters (Tlusty 2005), mangrove crabs (Todd et al 2011), cherry shrimp (Flores and Chien 2011), and tiger prawns (Wade et al 2014). This analysis proved to be a simple, yet effective method to measure color changes with the capacity to quantify and detect the light effects on animal coloration.…”

The combined effects of diet, environment and genetics on pigmentation in the Giant Tiger Prawn, Penaeus monodon

“…Colour of uncooked or cooked prawns was quantified using the average colour of 164 the first three abdominal segments measured using digital images and ImageJ 165 software (Schneider, et al, 2012), as used previously (Wade, et al, 2014) researchers. For all microscopy samples, the first abdominal segment was 178 removed from uncooked animals, the shell removed and chromatophores 179 photographed using a Leica M165C stereo microscope fitted with a Canon EOS 180 5D digital camera.…”

“…Past studies have shown that the methods used during harvesting farmed 399 prawns can have a significant impact on cooked prawn colour, and hence price of 400 farmed product (Wade, et al, 2014). The response of prawns to background 401 colour (Parisenti, et al, 2011b;Tume, et al, 2009) also suggests that harvesting 402 animals into black bins has the potential to rapidly improve prawn colour, but 403 also that harvesting into white bins may adversely affect cooked prawn colour.…”

“…Significant variation in the colour of farmed prawns has been 414 demonstrated between different ponds (Wade, et al, 2014), and this may 415 influence the response to substrate colour. An animal that is already very dark 416 may not show a strong response to dark substrates compared with an animal 417 that is less pigmented before exposure.…”