The texture of table olives

Dr Jeanette Purhagen
Perten Instruments, Sweden
jpurhagen@perten.com

The texture of table olives was investigated using compression, puncture and compression-cutting methods using Perten Instruments TVT.

Materials and Methods


Two samples of pitted black olives (low-cost and mid-cost) and one sample of green olives (mid-cost) were tested.

  • For texture measurements, a TVT was used with three different types of probes/rigs
    (Figure 1): Compression plate (CP) 35 mm diameter
  • Cylinder probe (CY) 2mm diameter
  • Jagged kernel probe (KP) 


Figure 1. (A) Compression plate (CP) 35 mm diameter probe; (B) Cylinder (CY) 2 mm diameter probe; (C) Kernel probe (KP).

Samples were bought at the supermarket and stored in jars at room temperature. Each sample was taken directly from the jar and placed centrally under the probe before measurement (9 to 11 replicates) (Tables 1–3).


Table 1. Compression plate method (larger size of green olives necessitated use of larger compression distance).


Table 2.
Cylinder penetration method


Table 3.
Kernel probe compression/cutting method

Results and Discussions

Compression plate
Black low-cost and green mid-cost olives were compressed without any structural breakage while black mid-cost olives burst to some extent during the compression (Figure 2, P1).

The greatest texture differences can be seen when comparing the total areas (total work of compression) and resilience (Table 4). For both measures the differences between the samples were significant (t-test, P = 0.05).


Table 4.
Compression plate force results, mean of replicates.


Figure 2.
Compression plate method curves for black and green olives (compression distance = 7.0 mm).

Cylinder penetration
The initial gradient (Figure 3) indicates the flattening of the olives under the applied force but there is no puncturing of the product.

Once a yield point is reached, the skin ruptures and the probe penetrates the flesh. Higher yield point (force required) indicates stronger skin. Black low-cost olives have the weakest skin and green mid-cost olives have the strongest skin. (Table 5, Figure 3, YP).

The distance of penetration before the skin ruptures indicates the elasticity of the skin and the flesh. Green mid-cost olives have skin with higher elasticity than black olives. (Table 5, Figure 3)

The force profile after the skin ruptures indicates penetration of the probe into the flesh of the olives. For black mid-cost olives, the force profile plateaus as the probe continues to penetrate the flesh at approximately constant force. (Figure 3).

Where the slope of the graph after the yield point changes, it indicates a different texture. For black mid-cost olives the clearly defined peak at skin rupture indicates a clear difference between skin firmness and flesh firmness. The longer distance to the yield point indicates that green mid-cost olives are more flexible than black olives. The higher force indicates that green mid-cost olives are firmer than black olives. The steeper initial slope indicates that black mid-cost olives are firmer than black low-cost and green mid-cost olives. (Figure 3)


Table 5: Cylinder penetration force results, mean of replicates.


Figure 3: Cylinder penetration method curves.

Kernel probe compression/cutting method


Table 6:
Kernel probe compression/cutting force results, mean of replicates
 

Figure 4:
Kernel probe compression/cutting method curves

Conclusions

All three methods and probes were able to differentiate between the different texture qualities of olives. The cylinder penetration method gave the clearest information about the skin and flesh of the olives. Texture analysis using the Perten Instruments TVT provided a fast, objective quality assessment of olives suitable for quality control applications.