A Method for the Preparation of Chicken Liver Pâté that Reliably Destroys Campylobacters

Abstract

This study devised a protocol for the manufacture of commercial quantities of chicken liver pâté that reliably destroyed campylobacters. A literature search identified 40 pâté manufacture recipes. Recipes stages with a potential to be antimicrobial were assembled to form a new protocol that included washing with organic acid, freeze-thaw and flambé in alcohol. Naturally-contaminated, high-risk livers were obtained from clearance flocks at slaughter and the effect of each stage of the protocol on Campylobacter populations was determined. Organic acid washing changed the color of the liver surfaces. However, there were no significant differences between liver surface color changes when a range of concentrations of lactic acid and ethanoic acid washes were compared by reflective spectrophotometry. A 5% (w/v) acid wash reduced numbers of indigenous campylobacters by around 1.5 log₁₀ CFU/g for both acids. The use of a Bain Marie was found to more reproducibly apply heat compared with pan-frying. Antimicrobial recipe stages reduced the numbers of campylobacters, but not significantly if thermal processing was ineffective. Cooking to 63°C was confirmed to be a critical control point for campylobacters cooked in a Bain Marie. Organoleptic and sensory assessment of pâté determined an overall preference for pâté made from frozen livers.

Figure 1

Thermographs showing surface and internal temperatures (A and C) and corresponding visible images showing color and appearance (B and D) after cooking by pan frying in butter on a surface at 100 °C for 100 sec on each side of the liver (A) or in a Bain Marie of boiling water placed in an oven set to 130 °C for 45 min (B). Both sets of cooked livers were subject to 10–15 sec of cooling before the thermographs could be taken. The Bain Marie cooked pâté set only after cooling and was subject to rheological movements between image captures.

Figure 2

Typical temperatures achieved at the corners (yellow, black, red and green) and center (pink) of a terrine of macerated chicken livers during baking in a Bain Marie and during cooling after removal from the oven.

Figure 3

(A) The effect of immersing livers in water or organic acid (2 min for each solvent), milk (for 1 h) or organic acid immersion (2 min) followed by milk immersion (1 h) on the numbers of campylobacters present on chicken livers. (B) The effect of immersing livers in milk (for 1 h) followed by immersion in water or organic acid (2 min for each solvent) on the numbers of campylobacters present on chicken livers. For both experiments, final clearance livers were stored chilled at 2 °C for 48 h before the commencement of each treatment. Error bars are the standard error of the mean log count for both graphs.

Figure 4

The numbers of campylobacters present in chicken livers at each stage of a protocol used for the manufacture of chicken liver pâté. Livers were either stored chilled at 2 °C for 48 h (diagonal hatch) or frozen to −20 °C for 24 h and thawed for 24 h (speckled dots) before the commencement of pâté manufacture. Error bars are the standard error of the mean log. An asterisk (*) denotes a sample that did not contain campylobacters determined by enrichment.

Figure 5

The numbers of campylobacters present in chicken livers before and after cooking in a Bain Marie under worst-risk conditions. Fresh livers from final clearance birds were prepared only by blending with an equal mass of molten butter before cooking and refrigerated storage to determine recovery from sub-lethal injury. An asterisk (*) denotes a sample that did not contain campylobacters determined by enrichment.

Figure 6

The numbers of campylobacters remaining after imperfect cooking of contaminated livers to 60 °C or 63 °C. Livers were treated by washing in organic acid and exposed to essential oils (EO) and compared with livers that were not washed in organic acid or exposed to EO to determine if treatment conferred additional safeguards. Error bars are the standard error of the mean log. An asterisk (*) denotes a sample that did not contain campylobacters determined by enrichment.