Stanza 19: Skírnir offers golden apples to Gerðr in an attempt to win her for Freyr. The editor's note explicitly connects these to Iðunn's apples of youth.
Author's Note: Emendation of epli ellifu ‘eleven apples’ to epli ellilyfs ‘apples of old-age-healing’ would identify them as the gods’ youth-restoring apples, otherwise kept by the goddess Iðunn.
‘Eleven apples I have here, all golden,
these will I give you, Gerðr,
to buy your affection, so that you may say that Freyr
is the least loathsome one alive!’
Stanza 20: Gerðr rejects the offer of the eleven apples.
Gerðr said:
‘Eleven apples I will never take,
for any man’s wishes,
nor, while our life endures, shall Freyr and I
both dwell together!’
Chapter 25-27(p. 25): When introducing the goddess Idunn, the text explains her vital role and the function of her apples.
Idunn is his wife. She keeps in her casket apples which the gods have to feed on when they age, and then they all become young, and so it will go on right up to Ragnarok.’
Chapter 56(p. 60): As part of a deal to save his own life, Loki is forced by the jötunn Þjazi (in eagle form) to promise to lure Idunn out of Asgard with her apples.
...he said that Loki would never get free unless he vowed solemnly to get Idunn to come outside Asgard with her apples, and Loki accepted.
Chapter 56(p. 60): Loki tricks Idunn by telling her he has found apples worth having and that she should bring her own for comparison. This allows Þjazi to abduct her.
But at the agreed time Loki lured Idunn out through Asgard into a certain forest, saying that he had found some apples that she would think worth having, and told her she should bring her apples with her and compare them with these.
Chapter 56(p. 60): The immediate and dire consequences for the gods of losing the apples are described.
But the Æsir were badly affected by Idunn’s disappearance and soon became grey and old.
Chapter 16(p. 76): In a list of kennings (poetic names) for Loki, he is identified as the "thief from giants, of goat and Brisingamen and Idunn’s apples."
Chapter 18-22(p. 86): When listing the proper kennings for Idunn, her primary role is stated.
How shall Idunn be referred to? By calling her wife of Bragi and keeper of the apples, and the apples the Æsir’s old-age cure.