pH

One of the parameters responsible for meat quality is its pH. On the average,

ostrich meat has been classified as intermediate, i.e. of pH from regular (<5.8) to high

(>6.2) as measured 24 hours post-slaughter [Sales and Mellett 1996]. These values

were further confirmed by Otremba et al. [1999] and Majewska et al. [2009] and

make ostrich meat ideal for processing [Sales and Mellett 1996, Fisher et al. 2000]

even though its high pH could lead to elevated water-holding capacity [Sales 1994].

There are many factors influencing post-mortem pH of ostrich meat, among others the

slaughter method, stunning, bleeding, deboning, packaging and storage conditions

[Lambooij et al. 1999, Hoffman et al. 2008, 2009].

Post-mortem muscle pH drops rapidly due to glycogenolysis process during which

lactic acid is produced. Some ostrich muscles, especially the ambiens, iliofibuaris

and obturatorius medialis do not follow usual post-mortem pH drop pattern, but they

E. Poławska et al.

11

present rapid drop of pH during first 2 hours and then its increase to stabilization

[Balog et al. 2006]. Meat quality traits which are related to the post-mortem pH decline

are mainly: colour, moisture content and shelf life [Balog and Almeida Paz 2007].

Lambooij et al. [1999] observed that stunning with air pressure leads to lower pH,

especially of leg and breast muscles, compared to low electric shock, where pH has

been observed to be the highest after slaughter. This result is similar to that reported

by Sales et al. [1996], who concluded that ultimate pH in ostrich meat is reached

within 2-6 hours post-mortem. Due to the fast pH decline of ostrich meat the electric

stimulation is not necessary for the meat tenderness improvement [Mellett 1985],

although it might be a factor responsible for cold-shortening [Hoffman et al. 2008].

Those post-mortem pH changes differ ostrich meat from meat of all other red meatmuscled

animals.

The effect of an early post mortem low-voltage electrical stimulation of carcasses

on pH of ostrich meat was recently examined by Hoffman et al. [2009]. It resulted

in lower pH value after 45 min in the fillet and big drum muscles. However, after 24

hours this effect disappeared when compared to other muscles. Two types of deboning

considered here were investigated with regard to their effect on meat pH. Botha et

al. [2006] indicated that pH24 did not differ between hot- and cold-deboned ostrich

meat. However, during storage over 42 days significant differences in pH occurred

among individual muscles. Hoffman et al. [2005] found a positive correlation between

ostrich meat pH48 and its juiciness: after 48 hours of storage hot-deboned meat was

less juicy than cold-deboned. From the same study it was concluded that pH48 in hotdeboned

samples is negatively correlated with Warner-Bratzler SF, while positively

with tenderness evaluated by test panel. Hoffman et al. [2005] also observed that hotdeboned

muscles differed in pH measured at 1 and 4 hours after slaughter.

Another important pH-influencing factor is further processing (mostly type of

packaging) of the meat. Fernandez-Lopez et al. [2008] observed that the deepest

decline in pH and related decrease in lactic acid bacteria count were in the vacuumpackaged

samples as well as in the ones packaged in modified atmosphere. This was

in accordance with Gonzalez-Montalvo et al. [2007] who reported that pH was lower

in vacuum-packaged compared to air-packaged samples after 6 days of observations.

Seydim et al. [2006], however, suggest that only type of package affects the pH of

ostrich meat while the time of storage does not.

Finally, the highest pH value 24 hours post-mortem was reported of the darkest

meat with lowest percentage of drip loss and cooking loss [Hoffman et al. 2008].

Water-holding capacity and drip loss

Water-holding capacity (WHC) is the ability of meat to retain water during

applying of external forces, for example cutting, mincing and heating. Appearance

before cooking, cooking ability, juiciness during chewing and the total amount of

saleable meat are influenced by its WHC [Sales and Horbańczuk 1998]. Lambooij

Physical characteristics of ostrich meat

12

et al. [1999] reported WHC of ostrich meat to be lower than that of pork and chicken

meat [Uijtenboogaart 1997], but similar to veal and beef. However, ostrich steaks

are evaluated as drier then beef loin steaks [Harris 1994]. This might be the effect

of overcooking the former, which is related to their low intramuscular fat content

being the factor loosing up the microstructure. Balog et al. [2006] described a relation

between WHC and meat texture properties. If not cooked in too high temperature and

for too long ostrich meat does not loose too much water what provides it quite high

juiciness. Although moisture of ostrich meat is around 75% [Hoffman et al. 2005],

Walter et al. [2000] classified it as dry. They found ostrich meat to be dry and rated

lower then beef as a stew or when stir-fried, whether consumers knew the meat origin

used in the products or not.

WHC is tightly associated with muscle pH values. Botha et al. [2006] reported that

the rate of post mortem pH drop of muscles affected their WHC. It was also observed

that the higher the muscle ultimate pH, the lower is the decrease in WHC [Lawrie

1998]. After reaching a minimum, muscles pH tends to increase with progressing age

due to osmotic pressure. In this case WHC increased but denaturation of proteins

with time decreased this indicator. It was concluded by Tornberg [1996] that in beef

the more shortened muscle showed a higher cooking loss with lower WHC, while

peak SF got higher. This was found for hot-deboned ostrich meat, but disappeared in 5

days post-mortem. It does not influence the sale chances for that kind of meat because

consumers have seldom access to meat sooner than 7 days after slaughter.

There are some discrepancies between results related to WHC and pH24 values.

Majewska et al. [2009] found that none of those parameters differed between muscles.

Other authors, however, showed significant intermuscle differences with regard to

both indicators [Sales 1996, Hoffman et al. 2008]. In case of thawing losses significant

differences have been found between muscles (from 1.28 to 4.28%) - Majewska et al.

[2009].

Otremba et al. [1999] found from 3 to 11.5% drip loss for both intact and minced

ostrich meat which increased with post-slaughter time and peaked at day 14. It was

found by Gonzalez-Montalvo et al. [2007] that temperature of storage does not

influence this process, although the method of packaging does. Air-packaged samples

differed significantly from those packaged in vacuum. Not satisfying results were

found on day 3 for vacuum-packaged, day 6 for air-packaged and stored at 10°C

and day 9 for air-packaged samples stored at 4°C. Moreover, Hoffman et al. [2005]

concluded that hot deboning prevents weight loss that occurs due to evaporation

during chilling of the meat.

With regard to other meat quality characteristics Thomas et al. [2004] observed

that the percentage of drip and cooking losses showed opposite trends. When both SF

value and percentage of cooking losses increased, the drip loss decreased. Due to the

relation between muscle pH and other characteristics, when pH increased, the drip

loss decreased. This was related to ostrich meat characterized by dry structure and

high pH.

E. Poławska et al.

13

Shelf life and microbial load

Currently, when consumption of ostrich meat shows increasing tendency,

improvement of its hygienic safety and extension of shelf-life are crucial, both for the

local markets and for export [Gonzalez-Montalvo et al. 2007].

pH is the determining factor for meat microbial quality and its shelf life. The

characteristic pH value for ostrich meat which is around 6.0 is a good condition for the

development of microorganisms resulting in off-odour. Van Schalkwyk et al. [2005]

observed short shelf life and dark meat colour when a high pH occurred.

Also deboning method can change the shelf life of ostrich meat. Lawrie [1998]

found that in hot-deboned muscles where temperature decline is faster then in colddeboned

ones, it results in lower microbial spoilage of meat.

According to Capita et al [2006] storage temperature and time both affect the

microbial count of meat. The exclusion of oxygen influences total aerobic bacteria

count (Psychrotropic, Pseudomonas). In the cited study, time of storage influenced

all the microbial groups and pH values of ostrich meat. Significant differences in

microbial count were reported between day 0 and 9 of storage. Initial pH of the meat

in that study was 6.7 and no difference was observed in this parameter between day

0 and 9. It was concluded that poor microbial quality and high pH of ostrich meat

post-slaughter could be responsible for high microbial loads during storage. Storage

temperature (10°C) of air as well as of vacuum-packaged ostrich meat has significant

effect on microbial counts until day 6 of storage. Oxygen exclusion affects the

microbial quality of packaged ostrich meat from day 3 of storage. Joint vacuum and

low storage temperature improves microbial quality of ostrich meat.

Storage time is of importance for the tenderization process, however, it can also

promote an increase in bacteriological load of meat. According to Pollok et al. [1997]

ostrich fillets packaged under vacuum and refrigerated became unacceptable after 21

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