Passing muster: grading beef quality with light

2 December 2019:

How do you measure the tenderness, juiciness and flavour of beef without eating it? It’s a challenge faced by everyone from meat inspectors at abattoirs to consumers looking through a butcher’s window. And they’re all subjective – until now.

A team led by Prof Ewa Goldys from the Centre for Nanoscale BioPhotonics (CNBP) based at the University of New South Wales (UNSW) node in Sydney, report in the Journal of Biophotonics that they have developed a method of determining beef grades by firing ultraviolet light at small samples. Not only does it accurately grade the meat, it also quantifies molecular components of tissue including proteins, amino acids, aromatic compounds and vitamins.

“We have developed an analysis technique that can identify and grade beef faster and more objectively,” said Dr Saabah Mahbub, a Research Fellow at CNBP’s UNSW node who worked on the study. “It has real potential to remove the subjectivity from the current laborious meat grading methodology.”

When a beef carcass arrives at an abattoir, it is reviewed by an experienced inspector, or ‘grader’, who studies its compositional quality such as the lean-to-fat ratio, or palatability factors such as visual appearance, smell, firmness, juiciness, tenderness and flavour. They weigh the carcass, use a colour-coded flip chart with pictures of the grades of meat for comparison, and measure things like colour, hump height, ossification (which determines maturity), and amount of marbling (or fat content) of each area from which a cut will be made.

All of their data is entered into a computer checklist as numbers, based on the opinion of a grader and relying on consistent benchmarks established over years. It is a costly procedure, relying on experienced graders, and can take anything from three to 10 minutes per carcass; graders are also limited in how much time they can spend in refrigerated rooms.

However, the only really objective test is for the beef’s pH level. Meat & Livestock Australia set the maximum pH level at 5.7; anything above this tends to indicate ‘dark cutting meat’ with a coarse texture, a more purple appearance rather than the preferred bright red, and a reduced shelf life since bacteria grow more rapidly in a higher pH environment. The inspectors then grade each muscle (or cut) on eating quality from the pH range 5.3 to 5.7; the grade can be either an MSA-3, MSA-4 or MSA-5.

“The whole process is ultimately subjective,” said Dr Mahbub. “There are so many factors that can impact on the grading result. Even the pH of a carcass depends significantly on pH measuring technique, skill and experience of the inspector, and the pH will be different if you measure it two hours after slaughter versus four hours afterwards.”

The CNBP team conducted a battery of biochemical tests and microscope analyses of known MSA-3, MSA-4 and MSA-5 beef grades to measure, to a very precise level, each grade’s composition of various proteins, aromatic compounds, the amount of tryptophan amino acid (used in the synthesis of proteins), connective tissues (or collagens) and fat-soluble vitamins like A, D and K.

They then used ‘fluorescence spectroscopy’ to analyse ungraded beef samples: this involved firing beams of ultraviolet light at the samples to excite the electrons in the molecules of certain compounds, causing them to emit light at different wavelengths. The emission patterns generated allowed the researchers to decipher the beef’s molecular composition and measure quantities very precisely, then compare these to the results from known grades.

“The findings show that it is possible to use an ultraviolet fluorescence-based approach to grading beef, and eliminate the element of subjectivity in the system,” said Dr Mahbub. “From here, we can easily envisage the development of a low-cost, hand-held device that can be used widely in the meat industry … by graders, butchers and even consumers.”

CNBP is now talking to potential industry partners to develop a prototype of a handheld beef grader using their technique, with a view to eventually creating a commercial product that could not only speed up the process and remove subjectivity, but give deeper insights just what it is that makes the best and juiciest cuts.

Journal: Journal of Biophotonics

Publication Title: Autofluorescence excitation‐emission matrices as a quantitative tool for the assessment of meat quality

Authors: Kashif Islam, Saabah B. Mahbub, Sandhya Clement, Anna Guller, Ayad G. Anwer, Ewa M. Goldys

Summary: Commercially produced meat is currently graded by a complex and partly subjective multiparameter methodology; a quantitative method of grading, using small samples would be desirable. Here, we investigate the correlation between commercial grades of beef and spectral signatures of native fluorophores in such small samples. Beef samples of different commercial grades were characterized by fluorescence spectroscopy complemented by biochemical and histological assessment. The excitation‐emission matrices of the specimens reveal five prominent native autofluorescence signatures in the excitation range from 250 to 350 nm, derived mainly from tryptophan and intramuscular fat. We found that these signatures reflect meat grade and can be used for its determination.