Pre-slaughter administration of glycerol as carbohydrate precursor and osmotic agent to improve carcass and beef quality

Highlights

• Plasma parameters and liver glycogen levels were not altered by glycerol treatment. Glycerol given to young bulls did not modify carcass quality.

• Glycerol did not affect proximal composition, pH, colour or sensory beef quality.

• The WHC was improved by the administration of 1200 mL glycerol 24 h before slaughter.

• A similar effect was observed with both types of glycerol administration.

Abstract

Glycerol is a by-product from biodiesel production. This molecule is a carbohydrate precursor, thus it maintains the pH of beef at below 5.8 after slaughter, contributing to the prevention of Dry Firm Dark (DFD) meat. Furthermore, glycerol osmotic properties could contribute to alleviating the effects of some stress situations. The aim of this study was to evaluate the effect of administering crude glycerol (2 g kg⁻¹ body weight; via nasogastric tube or in drinking water) 24 h prior to the slaughter of young bulls, on plasma parameters, liver glycogen levels, carcass (body weight, dressing percentage, carcass weight and length), and beef quality (proximal composition, pH, colour, water holding capacity (WHC), drip loss, cooking loss, and sensory attributes). In general, the plasma parameters and liver glycogen were not affected by glycerol administration (P>0.05). Transport had a significant effect on total protein, albumin, glucose, sodium, potassium, chloride, and lactate plasma levels. Carcass parameters, proximal composition, pH, colour and sensory attributes were not affected (P>0.05) by glycerol treatment but WHC was (P<0.05). The glycerol did not affect the stress markers in plasma during the transport, carcass or meat quality negatively, but it seems to improve WHC of beef.

Introduction

Recent interest in biodiesel as a renewable energy resource has led to the production of large amounts of glycerol as a by-product. Several studies have identified animal feed as a possible use for unrefined glycerol (Della Casa et al., 2009, Lammers et al., 2008, Parsons et al., 2009), since the molecule may be converted into glucose (Mach et al., 2009). Glycerol is converted to propionate in the rumen (Mach et al., 2009), which is transformed into glucose and provide energy through the gluconeogenic pathway, and then is converted into glycogen in the liver. Glycogen is used as a substrate for postmortem lactic acid production in muscle and therefore the pH falls (Immonen and Puolanne, 2000). So it can produce sufficient pH decrease to reach the target value (=below 5.8) after slaughter, contributing to the prevention of Dry Firm Dark (DFD) meat, which causes substantial economic losses in the beef meat mark (Brandon, 2004). Indeed, some Spanish meat industries penalise carcass price with discounts of 30% when meat pH measured 24 h after slaughter is greater than 5.8 (Mach et al., 2008a). Previously, it was studied the administration of other substances previous slaughter, e.g. sorbitol, to prevent the incidence of this defect on meat (Bignon, 1992). Glycerol supplementation might therefore be considered for preventing the pH of beef from exceeding 5.8. Furthermore, osmotic properties have been attributed to glycerol (Parker et al., 2007). Research in human has shown that glycerol included in sports soft drinks increases water retention in high-performance athletes (Anderson et al., 2001, Wagner, 1999). The ingestion of this type of drink before exercise results in hyperhydration of the body cells so, in a parallel way, it could maintain body water content in stress situations, such as long distance transport (Parker et al., 2007), by which contributes to prevent water losses in meat, while improving some quality attributes like juiciness and tenderness (Offer and Knight, 1988).

In Bos indicus steers, Parker et al. (2007) concluded that glycerol administration at 2 g kg⁻¹ body weight (BW) before transport in a single dose, shows promise as a prophylactic treatment for attenuating the effects of long distance transportation by maintaining body water, decreasing the energy deficit and preserving health and muscle quality. However, the authors did not study the effect of glycerol on carcass or beef quality.

The hypothesis of this study was based on the glycerol role as carbohydrate precursor and osmotic molecule that could improve carcass and meat quality. Due to nasogastric tube administration is not a farm practice; administration in drinking water will be studied as an alternative. Higher levels of glucose in blood might be expected in the glycerol groups, because between 80% and 90% of glycerol is fermented in the rumen and provides propionate as a glucose precursor (Ramos and Kerley, 2012), so blood analyses were carried out. In addition, as glucose could be transformed into glycogen in liver and muscle, glycogen content was measured. Then, to evaluate the transport as stress situation, other parameters, as cortisol were studied. So, the aims of this research were to study the effect of pre-slaughter glycerol administration by nasogastric tube or in drinking water on plasma parameters, liver glycogen levels, carcass parameters and beef quality in young bulls.